Aquatic Habitats (Insects)

Less than 3% of the world’s total water occurs on land, and most of this is frozen in polar ice caps. Streams and rivers are one of the more conspicuous features of the landscape; however, their total area is about 0.1% of the land surface, whereas lakes represent about 1.8% of the total land surface. Some authors have questioned whether insects have been successful in water because aquatic species represent only a small portion of the total hexapod fauna. However, 13 orders of insects contain species with aquatic or semiaquatic stages, and in 5 of these (Ephemeroptera, Odonata, Plecoptera, Megaloptera, and Trichoptera) all species are aquatic with few exceptions (Table I). Few aquatic insects spend all of their life in water; generally any insect that lives in water during a portion of its development is considered to be ” aquatic.” Usually, but not always, for most “aquatic” species, it is the larval stage that develops in aquatic habitats, and the adults are terrestrial (Table I). The pupae of some taxa undergoing complete metamorphosis (i.e., holometabo-lous) remain within the aquatic habitat; in others the last larval instar moves onto land to pupate, providing the transition stage from the aquatic larva to the terrestrial adult.


Occurrence of Life Stages in Major Habitat Types for Aquatic and Semiaquatic Representatives of Insect Orders

Order Terrestrial Freshwater
Collembola A, L A, L
Ephemeroptera A L
Odonata A L
Heteroptera A A, L
Orthoptera A, L A, L
Plecoptera A L
Coleoptera A, L, P A, L
Diptera A, P L, P
Hymenoptera A A, L, P
Lepidoptera A L, P
Megaloptera A, P L
Neuroptera A, P L
Trichoptera A L, P

Modified from Ward, J. V. (1992). “Aquatic Insect Ecology,” Vol. 1, “Biology and Habitat.” Wiley, New York. A, adult; L, larvae; P, pupae.
The success of insects in freshwater environments is demonstrated by their diversity and abundance, broad distribution, and their ability to exploit most types of aquatic habitat. Some species have adapted to very restricted habitats and often have life cycles, morphological, and physiological adaptations that allow them to cope with the challenges presented by aquatic habitats. One aquatic environment in which insects have not been very successful is saltwater habitats, although some 14 orders and 1400 species of insects occur in brackish and marine habitats; only one group occurs in the open ocean. One of the most widely accepted attempts to explain why more insects do not live in marine environments is that successful resident marine invertebrates evolved long before aquatic insects and occupy many of the same niches inhabited by freshwater insects. Thus, marine invertebrates, such as crustaceans, have barred many insects from marine habitats by competitive exclusion. Problems with osmoregulation have been given as another reason for the paucity of saltwater species; however, one of the two multicellular animals found in the Great Salt Lake is a member of the order Diptera (see Section Unusual Habitats), providing evidence that some insects display a strong ability to osmoregulate.
The first aquatic insects are believed to have inhabited flowing water as early as the Permian and Triassic. It was not until the late Triassic and early Jurassic that evidence of abundant lentic, or still-water, fauna arose, accompanied by rapid diversification of water beetles, aquatic
bugs (Heteroptera), and primitive Diptera. On the basis of several lines of evidence including osmoregulation, fossil evidence, secondary invasions to water of many taxa, and great variation in gill structure among and within orders, some authors have suggested that the first insects may have lived in water rather than in terrestrial habitats. However, the general consensus is that an aquatic origin for insects seems unlikely and that aquatic insects may not have shown up until 60- 70 million years later than their terrestrial counterparts.
Freshwater systems are often divided into standing (lentic) and flowing (lotic) waters. Although such a division is useful for indicating physical and biological differences, habitat diversity can vary tremendously within these two broad categories, and some of the same taxa may be found in both lentic and lotic habitats, depending on the physiological constraints of a given habit. Many factors influence successful colonization of aquatic insects to a given habitat; however, most of these would fall under four broad categories: (1) physiological constraints (e.g., oxygen demands, respiration, osmoregulation, temperature effects), (2) trophic considerations (e.g., food acquisition), (3) physical constraints (e.g., coping with harsh habitats), and (4) biotic interactions (e.g., predation, competition). However, these categories are so interrelated that detailed analysis of each factor separately is very difficult.


The classification system used here for lotic and lentic habitats stresses the basic distinction between flowing water (i.e., streams, rivers) and standing-water (i.e., ponds, lakes, swamps, marshes) habitats (Table II). This separation is generally useful in describing the specific microhabitats (e.g., sediments, vascular hydrophytes, detritus) in which aquatic insects may be found. Both stream/river currents and lake shoreline waves often create erosional (riffle-type) habitats and may resemble each other in their physical characteristics, whereas river floodplain pools and stream/river backwaters create depositional (pool-type) habitats that may resemble lake habitats as well (Table II). Within a given habitat, the modes by which individuals maintain their location (e.g., clingers on surfaces in fast-flowing water, sprawlers on sand or on surfaces of floating leaves, climbers on stem-type surfaces, burrowers in soft sediments) or move about (e.g., swimmers, divers, surface skaters) have been categorized (Table III). The distribution pattern resulting from habitat selection by a given aquatic insect species reflects the optimal overlap between habit and physical environmental conditions that comprise the habitat, such as bottom type, flow, and turbulence. Because


Aquatic Habitat Classification System

General category Specific category Description
Lotic—erosional (running-water riffles) Sediments Coarse sediments (cobbles, pebbles, gravel) typical of stream riffles.
Vascular hydrophytes Vascular plants growing on (e.g., moss, Fontinalis) or among (e.g., pond-weed, Potamogeton pectinatus) coarse sediments in riffles.
Detritus Leaf packs (accumulations of leaf litter and other coarse particulate detritus at leading edge or behind obstructions such as logs or large cobbles and boulders) and debris (e.g., logs, branches) in riffles.
Lotic—depositional (running-water pools and margins) Sediments Fine sediments (sand and silt) typical of stream pools and margins.
Vascular hydrophytes Vascular plants growing in fine sediments (e.g., Elodea, broad-leaved species of Potamogeton, Ranunculus).
Detritus Leaf litter and other particulate detritus in pools and alcoves (backwaters).
Lentic—limnetic (standing water) Open water On the surface or in the water column of lakes, bogs, ponds.
Lentic—littoral (standing water, shallow-water area) Erosional Wave-swept shore area of coarse (cobbles, pebbles, gravel) sediments.
Vascular hydrophytes Rooted or floating (e.g., duckweed, Lemna) aquatic vascular plants (usually with associated macroscopic filamentous algae).
Emergent zone Plants of the immediate shore area (e.g., Typha, cattail), with most of the leaves above water.
Floating zone Rooted plants with large floating leaves (e.g., Nymphaea, pond lily), and nonrooted plants (e.g., Lemna).
Submerged zone Rooted plants with most leaves beneath the surface.
Sediments Fine sediments (sand and silt) of the vascular plant beds.
Freshwater lakes Moist sand beach areas of large lakes.
Lentic—profundal (standing water, basin) Sediments Fine sediments (fine sand, silt, and clay) mixed with organic matter of the deeper basins of lakes. (This is the only category of “lentic—profundal.”)
Beach zone Marine intertidal Rocks, sand, and mud flats of the intertidal zone.


Categorization of Aquatic Insect Habits: That Is, Mode of Existence


Adapted for “skating” on the surface where they feed as scavengers on organisms trapped in the surface film (e.g.,
Heteroptera: Gerridae, water striders).

Inhabiting the open-water limnetic zone of standing waters (lentic; lakes, bogs, ponds). Representatives may float and
swim about in the open water but usually exhibit a diurnal vertical migration pattern (e.g., Diptera: Chaoboridae, phantom
midges) or float at the surface to obtain oxygen and food, diving when alarmed (e.g., Diptera: Culicidae, mosquitoes).

Adapted for swimming by “rowing” with the hind legs in lentic habitats and lotic pools. Representatives come to the surface
to obtain oxygen, dive and swim when feeding or alarmed; may cling to or crawl on submerged objects such as vascular
plants (e.g., Heteroptera: Corixidae, water boatman; Coleoptera: adult Dytiscidae, predaceous diving beetles).

Adapted for “fishlike” swimming in lotic orlentic habitats. Individuals usually cling to submerged objects, such as rocks (lotic
riffles) or vascular plants (lentic) between short bursts of swimming (e.g., Ephemeroptera: Siphlonuridae, Leptophlebiidae).

Representatives have behavioral (e.g., fixed retreat construction) and morphological (e.g., long, curved tarsal claws, dorsov-
entral flattening, ventral gills arranged as a sucker) adaptations for attachment to surfaces in stream riffles and wave-swept
rocky littoral zones of lakes (e.g., Ephemeroptera: Heptageniidae; Trichoptera: Hydropsychidae; Diptera: Blephariceridae).

Inhabiting the surface of floating leaves of vascular hydrophytes or fine sediments, usually with modifications for staying on top
of the substrate and maintaining the respiratory surfaces free of silt (e.g., Ephemeroptera: Caenidae; Odonata: Libellulidae).

Adapted for living on vascular hydrophytes or detrital debris (e.g., overhanging branches, roots and vegetation along streams,
submerged brush in lakes) with modifications for moving vertically on stem-type surfaces (e.g., Odonata: Aeshnidae).

Inhabiting the fine sediments of streams (pools) and lakes. Some construct discrete burrows that may have sand grain
tubes extending above the surface of the substrate or the individuals may ingest their way through the sediments (e.g.,
Ephemeroptera: Ephemeridae, burrowing mayflies; Diptera: most Chironominae, Chironomini, bloodworm midges). Some
burrow (tunnel) into plants stems, leaves, or roots (miners).

food in aquatic habitats is almost always distributed in a patchy fashion, the match between habitat and habit is maximized in certain locations. This combination will often result in the maximum occurrence of a particular species.
In view of the complex physical environment of streams, it is not surprising that benthic invertebrates have evolved a diverse array of morphological adaptations and behavioral mechanisms for exploiting foods. Throughout this article we will follow the functional classification system originally described by K. W. Cummins in 1973, which is based on the mechanisms used by invertebrates to acquire foods (Table IV). These functional groups are as follows:
• Shredders, which are insects and other animals that feed directly on large pieces of organic matter (e.g., decomposing leaves and fragments of wood >1mm in size) and their associated fungi and bacteria, and convert them into fine particulate organic matter (FPOM) through maceration, defecation, and physical degradation.
• Collector-filterers, which have specialized anatomical structures (e.g., setae, mouth brushes, fans, etc.) or silk and silklike secretions that act as sieves to remove fine particulate matter less than 1 mm in diameter from the water column.
• Collector-gatherers, which gather food, primarily FPOM, that is deposited within streams or lakes.
• Scrapers, which have mouthparts adapted to graze or scrape materials (e.g., periphyton, or attached algae, and the associated microbes) from rock surfaces and organic substrates.
• Predators, which feed primarily on other animals by either engulfing their prey or piercing prey and sucking body contents.
These functional feeding groups refer primarily to modes of feeding or the means by which the food is acquired, and the food type per se ( Table IV). For example, shredders may select leaves that have been colonized by fungi and bacteria; however, they also ingest attached algal cells, protozoans, and various other components of the fauna along with the leaves.


Streams vary greatly in gradient, current velocity, width, depth, flow, sinuosity, cross-sectional area, and substrate type, depending on their position in the landscape with respect to geology, climate, and the basin area they drain. Anyone who has spent much time around or wading in streams is aware that these can be extremely diverse habitats, often manifesting great differences over short distances. In the upper reaches of a catchment or drainage basin, small streams often display a range of habitats characterized by areas that are shallow, with fast flow over pebbles, cobbles, and boulders. There are also areas with steep gradients, cascades, or waterfalls when the underlying substrate is bedrock. There also may be areas of slow velocity in pools of deeper water.
In many streams draining forested watersheds, pools are found. Pools are depositional areas during normal flow as organic and inorganic particles settle to the substrate, and a similar settling process often occurs in side channels or backwater areas of streams. Pools are also created upstream of large instream pieces of wood, which may form obstructions known as debris dams. Because pools are generally characterized by reduced water velocity, many of the small particles normally suspended in fast flows settle to the bottom. In many low-gradient streams, including large rivers, bottom substrate often consists of silt, sand, and gravel-sized particles that are frequently moved by the force of the flowing water. In such systems, large pieces of woody debris entering the river from bank erosion or


General Classification Systems for Aquatic Insect Trophic Relations

Subdivision of function group

Functional group”
Dominant food
Feeding mechanism
Examples of taxa
General particle size
range of food ([tm)

Living vascular hydrophyte plant
Herbivores—chewers and
miners of live macrophytes


Decomposing vascular plant tissue


and wood—coarse particular organic


matter (CPOM)









Detritivores—filterers or

suspension feeders
Decomposing fine particular organic


matter (FPOM)



Detritivores—gatherers or

deposit (sediment) feeders

(includes surface film feeders)


Periphyton—attached algae and
Herbivores—grazing scrapers
associated material
or mineral and organic surfaces





Living animal tissue
Carnivores — attack prey, pierce


tissues and cells, suck fluids


Living animal tissue
Carnivores—ingest whole
animals (or parts)






from adjacent floodplain or upstream areas may represent an important habitat for invertebrate colonization.
Substratum characteristics are often perceived as a major contributor to the distribution of many invertebrates; however, many other factors, including water velocity, food, feeding habits, refuge, and respiratory requirements, can be associated with specific substrates. Substratum particle size is influenced by several items, including geology, physical characteristics of the rock, past and present geo-morphic processes (flowing water, glaciation, slope, etc.), climate and precipitation, and length of time over which the processes occur. These in turn influence landform, which exerts a major influence on
various hydrological characteristics of aquatic habitats. Unlike many lentic environments, in lotic systems the velocity of moving water is sufficient to pass the water around the body of an insect and turbulence provides reaeration; thus, dissolved oxygen is rarely limiting to stream inhabitants. Local transport and storage of inorganic and organic materials by the current may be either detrimental (e.g., scouring action) or beneficial (as a food source). For example, most aquatic insects in flowing waters are passive filter feeders and depend on the water current for delivery of their food. Scouring flows may therefore remove from the streambed large organic particles (e.g., leaves) as well as smaller ones, creating temporary reductions in food supplies. In contrast, moderately rapid flows may facilitate feeding of some scraper or grazer insects by preventing excessive sedimentation buildup on the surfaces on which they feed.

Some Insects and Their Adaptations to Erosional Habitats

Adaptations of aquatic insects to torrential or “rapid flow” habitats include the dorsoventral flattening of the body, which serves two purposes: it increases the organism’s area of contact with the surface substratum, and it offers a mechanism by which animals can remain in the boundary layer when water velocity diminishes, thereby reducing drag under subsequent exposure to high velocities. However, this second idea may be an oversimplification. Indeed, some authors have suggested that the dorsoventrally flattened shape may actually generate lift in the insect. Examples of animals inhabiting stones in torrential habitats include a number of mayflies (Ephemeroptera) belonging to the families Heptageniidae (Fig. 1A) and Ephemerellidae; some Plecoptera, such as Perlidae (Fig. 1G); some Megaloptera (i.e., Corydalidae) (Fig. 1D); and caddisflies (Trichoptera), such as Leptoceridae (Ceraclea).
 Typical insects inhabiting lotic environments. (A) Ephemeroptera: Heptageniidae (Rhithrogena). (Photograph by H. V. Daly.) (B) Diptera: Simuliidae (Simulium), (C) Trichoptera: Limnephilidae (Dicosmoecus), (D) Megaloptera: Corydalidae (Corydalus), (E) Diptera: Tipulidae (Tipula), (F) Plecoptera: Pteronarcyidae (Pteronarcys), (G) Plecoptera: Perlidae, (H) Coleoptera: Psephenidae (Psephenus).
FIGURE 1 Typical insects inhabiting lotic environments. (A) Ephemeroptera: Heptageniidae (Rhithrogena). (Photograph by H. V. Daly.) (B) Diptera: Simuliidae (Simulium), (C) Trichoptera: Limnephilidae (Dicosmoecus), (D) Megaloptera: Corydalidae (Corydalus), (E) Diptera: Tipulidae (Tipula), (F) Plecoptera: Pteronarcyidae (Pteronarcys), (G) Plecoptera: Perlidae, (H) Coleoptera: Psephenidae (Psephenus).
“n addition to body shape, many mayflies and stoneflies have legs that project laterally from the body, thereby reducing drag and simultaneously increasing friction with the substrate. Most of these taxa are either scrapers or gatherers on surfaces of stones or predators on other aquatic insects. Undoubtedly, the diverse physical forces encountered in aquatic environments, especially streams, influence the array of morphologies found among aquatic insects.
In some caddisflies (e.g., Glossosomatidae), the shape of the case rather than the insect is modified. The larvae of Glossosomatidae in their tortoiselike cases are frequently seen grazing on the upper surfaces of stones in riffle areas. Another curious caddisfly grazer on stone surfaces is Helicopsyche , whose larvae construct coiled cases of sand grains shaped like snail shells. Both glossosomatids and helicopsychids reach their greatest abundances in sunny cobble riffles, where they feed on attached periphyton or algae. Another lotic insect that relies on a rather streamlined case is the limnephilid cad-disfly Dicosmoecus (Fig. 1C).
Larvae of the dipteran family Blephariceridae are unusual in that they possess hydraulic suckers. A V-shaped notch at the anterior edge of each of the six ventral suckers works as a valve out of which water is forced when the sucker is pressed to the substrate. The sucker operates as a piston with the aid of specialized muscles. In addition, a series of small hooks and glands that secrete a sticky substance aid sucker attachment as the larvae move in a zigzag fashion, releasing the anterior three suckers, lifting the front portion of the body to a new position, and then reattaching the anterior suckers before releasing and moving the posterior ones to a new position. These larvae are commonly found on smooth stones in very rapid velocities and are usually absent from stones covered with moss and from roughened stones that interfere with normal sucker function. Several other aquatic insects have structures that simulate the action of suckers. The enlarged gills of some mayflies (e.g., Epeorus sp. and Rhithrogena sp.: Fig. 1A) function as a friction pad, and Drunella doddsi has a specialized abdominal structure for the same purpose. Some chironomids have “pushing prolegs” represented by circlet of small spines that function as a false sucker when pressed to the substrate. Mountain midge larvae (Deuterophlebiidae) possibly use a similar mechanism to attach their suckerlike prolegs. Most of these animals are primarily grazers on thin films of epilithon (algae, associated fine organic matter, and microbes) found on the surface of stones.
Flowing water usually carries many organic (and inorganic) particles and a number of insects exploit these suspended particles. Filter-feeding collectors (Table IV) exploit the current for gathering food with minimal energy expenditure. For example, certain filtering collectors exploit locations where flows converge over and around substrates, thus allowing the animals to occupy sites of greater food delivery. Examples include caddisfly larvae belonging to the families Hydropsychidae and Brachycentridae. Silk is used for attachment by a number of caddisflies (e.g., Hydropsychidae, Philopotamidae, and Psychomyiidae), which build fixed nets and retreats (Fig. 2A). Although the Philopotamidae are found in riffle habitats, their fine-meshed, tubelike nets are usually found in crevices or undersides of stones in low velocity microhabitats (Fig. 2C). The nets of the caddisfly, Neureclipsis, are limited to moderately slow (<25cms_1) velocities and the large (up to 20 cm long), trumpet-shaped nets ( Fig. 2D) are used to capture small animals drifting downstream. Neureclipsis larvae are often very abundant in some lake outflow streams where drifting zooplankton are abundant.
Some case-making caddisflies (e.g., Brachycentrus sp.) also use silk for attaching their cases to the substrate in regions of moderately
Representative lotic insects in their environment. (A) Caddisfly larva (Macrostenum) in its retreat grazing on materials trapped on its capture net, (B) mayfly larva of Hexagenia (Ephemeridae) in its U-shaped burrow, (C) tubelike nets of phi-lopotamid caddisfly larvae (Philopotamidae) on the lower surface of a stone, (D) the caddisfly larva and cornucopia-shaped net of Neureclipsis (Polycentropodidae).rapid flow. Many chironomid larvae construct fixed silken retreats for attachment or silken tubes that house the larvae, with a conical catchnet spun across the lumen of the tube. Periodically, the larva devours its catchnet with adhering debris that has been swept into the burrow by the water currents. Meanwhile, other chironomid larvae such as Rheotanytarsus spp. construct small silk cases that are attached to the stream substratum with extended hydralike arms. The arms project up in the current and are smeared with a silklike secretion to capture particles.
FIGURE 2 Representative lotic insects in their environment. (A) Caddisfly larva (Macrostenum) in its retreat grazing on materials trapped on its capture net, (B) mayfly larva of Hexagenia (Ephemeridae) in its U-shaped burrow, (C) tubelike nets of phi-lopotamid caddisfly larvae (Philopotamidae) on the lower surface of a stone, (D) the caddisfly larva and cornucopia-shaped net of Neureclipsis (Polycentropodidae).rapid flow. Many chironomid larvae construct fixed silken retreats for attachment or silken tubes that house the larvae, with a conical catchnet spun across the lumen of the tube. Periodically, the larva devours its catchnet with adhering debris that has been swept into the burrow by the water currents. Meanwhile, other chironomid larvae such as Rheotanytarsus spp. construct small silk cases that are attached to the stream substratum with extended hydralike arms. The arms project up in the current and are smeared with a silklike secretion to capture particles.
Larval blackflies (Simuliidae; Fig. 1B) use a combination of hooks and silk for attachment. The thoracic proleg resembles that of chironomids and deuterophlebiids, described earlier, and the last abdominal segment bears a circlet of hooks, which it uses to anchor itself to substrates. The larva moves forward, inchwormlike, spins silk over the substrate, and attaches the proleg and then the posterior circlet of hooks to the silken web. Most blackfly larvae possess well-developed cephalic fans, which are used to filter small particles from suspension. These attached larvae twist their bodies longitudinally from 90° to 180° with the ventral surface of the head and fans facing into the current. The fusiform body shape of blackfly larvae reduces turbulence and drag around their bodies, which are often located in regions of relatively rapid flow. Blackfly pupae are housed in silken cases that are attached to the substrate.
Although unidirectional current is the basic feature of streams, most lotic insects have not adapted to strong currents, but instead have developed behavior patterns to avoid current. Very few lotic insects are strong swimmers, probably because of the energy expenditure required to swim against a current. Downstream transport or drift requires only a movement off the substrate to enter the current. Streamlined forms, such as the mayflies Baetis spp., Centroptilum, Isonychia spp., and Ameletus spp., are capable of short, rapid bursts of swimming, but most lotic insects move by crawling or passive displacement. One characteristic of these latter mayflies is the possession of a fusiform, or streamlined, body shape: examples include several Ephemeroptera such as Baetis, Centroptilum, and Isonychia, as well as a number of beetle (Coleoptera) larvae. A fusiform body shape reduces resistance in fluids, and within the mayflies the shape is often associated with excellent swimming abilities.
The benthic fauna in streams often can be found in cracks and crevices, between or under rocks and gravel, within the boundary layer on surfaces, or in other slack-water regions. Another method of avoiding fast currents is living in debris accumulations consisting of leaf packs and small woody debris. This debris offers both a food resource and a refuge for insects and contains a diverse array of aquatic insects including stoneflies such as Peltoperlidae and Pteronarcyidae (Fig. 1F), caddisflies such as Lepidostomatidae and some Limnephilidae, as well as dipterans such as chironomids and tipulid crane flies (Fig. 1E).
In some streams with unstable sandy or silt substrates, woody debris can represent a “hot spot” of invertebrate activity. Wood debris provides a significant portion of the stable habitat for insects in streams when the power of the flowing water is insufficient to transport the wood out of the channel. In addition to the insect component using wood primarily as a substrate, there is often a characteristic xylophilus fauna associated with particular stages of wood degradation. These include chironomid midges and scraping mayflies (Cinygma spp. and Ironodes spp.) as early colonizers, and larvae and adults of elmid beetles. In western North America, an elmid (Lara avara) and a caddisfly (Heteroplectron) are gougers of firm waterlogged wood, chironomids are tunnelers, and the tipulids, Lipsothrix spp., are found in wood in the latest stages of decomposition. Woody debris is most abundant in small, forested watersheds, but it is also an important habitat in larger streams with unstable beds. In the southeastern coastal plain of the United States and in low-gradient mid- and southwestern streams and rivers with unstable bottom substrate, woody debris or “snags” often represent the major habitat for aquatic insect abundance and biomass. High populations and biomass of filter-feeding animals such as net-spinning caddisflies (Hydro-psyche spp., Cheumatopsyche spp., and Macrostenum) (Fig. 2A), and blackflies occur in these streams and rivers. In addition to filter feeders, other groups such as odonates, mayflies, stone-flies, elmid beetles, nonfiltering caddisflies, and dipteran larvae can be locally abundant on large pieces of woody debris. Invertebrate shredders and scrapers promote decomposition of outer wood surfaces by scraping, gouging, and tunneling through wood. In fact, wood gouging habits of some net-spinning caddisflies have been blamed for the failure of submerged timber pilings that had been supporting a bridge!
Sand and silt substrates of rivers and streams are generally considered to be poor habitats because the shifting streambed affords unsuitable attachment sites and poor food conditions. An extreme example of this instability is the Amazon River, where strong currents move the bedload downstream, resulting in dunes of coarse sand up to 8 m in height and 180 m in length, thus largely preventing the establishment of a riverbed fauna. However, sandy substrates do not always result in poor habitat for all aquatic insects: some sandy streams are quite productive. Blackwater (i.e., high tannic acid concentrations from leaf decomposition) streams of the southeastern United States have extensive areas of sand, with some of insects, such as small Chironomidae (<3mm in length), exceeding 18,000m-2 in abundance. Their food is derived from fine organic matter, microbes, and algae trapped in the sandy substrate. Numerically, the inhabitants of sandy or silty areas are mostly sprawlers or burrowers, with morphological adaptations to maintain position and to keep respiratory surfaces in contact with oxygenated water. At least one insect, the mayfly Ametropus, is adapted for filter feeding in sand and silt substrates of large rivers. Ametropus uses the head, mouthparts, and forelegs to create a shallow pit in the substrate, which initiates a unique vortex (flow field in which fluid particles move in concentric paths) in front of the head and results in resuspension of fine organic matter as well as occasional sand grains. Some of these resuspended fine particles are then trapped by fine setae on the mouthparts and forelegs. Many predaceous gomphid (Odonata) larvae actually burrow into the sediments by using the flattened, wedge-shaped head and fossorial (adapted for digging) legs. The predaceous mayflies Pseudiron spp. and Analetris spp. have long, posterior-projecting legs and claws that aid in anchoring the larvae as they face upstream. Some mayflies (e.g., Caenidae and Baetiscidae) have various structures for covering and protecting gills, and others (e.g., Ephemeridae, Behningiidae) have legs and mouthparts adapted for digging. The predaceous mayfly Dolania spp. burrow rapidly in sandy substrates and have dense setae located at the anterior-lateral corners of the body as well as several other locations. The larva uses its hairy body and legs to form a cavity underneath the body where the ventral abdominal gills are in contact with oxygenated water.
Dense setae also are found in burrowing mayflies belonging to the family Ephemeridae that are common inhabitants of sand and silt substrates. They construct shallow U-shaped burrows and use their dorsal gills to generate water currents through the burrow (Fig. 2B” , while using their hairy mouthparts and legs to filter particles from the moving water. Hairy bodies seem to be a characteristic of many animals dwelling on silt substrates, which include other collector mayflies such as Caenis, Anepeorus, and some Ephemerellidae.
Many dragonflies (e.g., Cordulegaster spp., Hagenius spp., and Macromiidae) have flattened bodies and long legs for sprawling on sandy and silty substrates. Some caddisflies, such as Molanna, have elongate slender bodies but have adapted to sand and silt substrates by constructing a flanged, flat case. They are camouflaged by dull color patterns and hairy integuments that accumulate a coating of silt. The eyes, which cap the anterolateral corners of the head, are elevated over the surrounding debris. The genus Aphylla (Gomphidae) is somewhat unusual in that the last abdominal segment is upturned and elongate, allowing the larvae to respire through rectal gills while buried fairly deep in mucky substrate. Some insects burrow within the upper few centimeters of the substratum in depo-sitional areas of streams. This practice is found among some drag-onflies and a number of caddisflies, including Molanna, and various genera of the families Sericostomatidae and Odontoceridae.

Specialized Flowing Water Habitats

The hyporheic region is the area below the bed of a stream where interstitial water moves by percolation. In gravelly substrates or glacial outwash areas, it may also extend laterally from the banks. In some situations, an extensive fauna occurs down to 1 m in such substrates. Most orders are represented, especially taxa with slender flexible bodies or small organisms with hard protective exoskeletons. Some stoneflies in the Flathead River of Montana spend most of their larval period in this extensive subterranean region of flow adjacent to the river. Stonefly larvae have been collected in wells over 4 m deep, located many meters from the river. Rivers draining glaciated regions where there are large boulders and cobble appear to have an exceptionally well-developed hyphoreic fauna.
Other specialized flowing water habitats include the madi-colous (or hygropetric) habitats, which are areas in which thin sheets of water flow over rock. These often approach vertical conditions (e.g., in waterfalls) and have a characteristic fauna. Among common animals in these habitats are caddisflies, including several microcaddisflies (Hydroptilidae), Lepidostomatidae, beetles such as Psephenidae, and a number of Diptera larvae belonging to the Chironomidae, Ceratopogonidae, Thaumaleidae, Tipulidae, Psychodidae, and some Stratiomyidae.
Thermal (hot) springs often have a characteristic fauna, which is fueled by algae and bacteria adapted to high temperatures. The common inhabitants include a number of dipteran families such as Chironomidae, Stratiomyidae, Dolichopodidae, and Ephydridae, as well as some coleopterans. A number of these survive within rather narrow zones between the thermal spring and cooler downstream areas.


Lentic or standing-water habitats range from temporary pools to large deep lakes and include marshes and swamps, as well as natural (i.e., tree holes, pitcher plants) and artificial (i.e., old tires, rain barrels) containers. The available habitats and communities for insects in a pond or lake were defined in Table II ” These habitats include the littoral zone, which comprises the shallow areas along the shore with light penetration to the bottom and normally contains macro-phytes (rooted vascular plants). The limnetic zone is the open-water area devoid of rooted plants, whereas the deeper profundal zone is the area below which light penetration is inadequate for plant growth, water movement is minimal, and temperature may vary only slightly between summer and winter. The aquatic and semiaquatic insect communities inhabiting these zones are known as the pleuston (organisms associated with the surface film), plankton and nekton (organisms that reside in the open water), and benthos (organisms associated with the bottom, or solid-water interface). Nektonic forms are distinguished from plankton by their directional mobility, and the latter are poorly represented in lentic waters by insects; the majority of insects found in standing-water habitats belong to the benthos. Their composition and relative abundance is dependent on a variety of factors, some of which are integrated along depth profiles. The overall taxonomic richness of benthic insect communities generally declines with increasing depth.
Among the aquatic communities of lentic habitats, the following orders of aquatic and semiaquatic insects are commonly found within the littoral, limnetic, and profundal zones: the springtails (Collembola), mayflies (Ephemeroptera), true bugs (Heteroptera), caddisflies (Trichoptera), dragonflies (Anisoptera) and dam-selflies (Zygoptera), true flies (flies, gnats, mosquitoes, and midges) (Diptera), moths (Lepidoptera), alderflies (Megaloptera), and beetles (Coleoptera). Not all these groups occur in lakes, and many are associated with ponds or marshes; examples of typical lentic insects are shown in Figs. 3 and 4 .
Typical insects inhabiting lentic environments. (A) Diptera: Chaoboridae (Chaoborus), (B) Trichoptera: Limnephilidae (Limnephilus), (C) Coleoptera: Dytiscidae (Agabus), (D) Coleoptera: Dytiscidae.
FIGURE 3 Typical insects inhabiting lentic environments. (A) Diptera: Chaoboridae (Chaoborus), (B) Trichoptera: Limnephilidae (Limnephilus), (C) Coleoptera: Dytiscidae (Agabus), (D) Coleoptera: Dytiscidae.
Typical insects inhabiting lentic environments. (A) Coleoptera: Hydrophilidae (Hydrochara). (Photograph by M. Higgins.) (B) Diptera: Chironomidae (Chironomus), (C) Odonata: Libellulidae (Pantala).
FIGURE 4 Typical insects inhabiting lentic environments. (A) Coleoptera: Hydrophilidae (Hydrochara). (Photograph by M. Higgins.) (B) Diptera: Chironomidae (Chironomus), (C) Odonata: Libellulidae (Pantala).

The Pleuston Community

The unique properties of the water surface or air-water interface constitute the environment of the pleuston community. The Collembola, or springtails, are small in size, have a springing organ (furcula), and a water-repelling cuticle that enables them to be supported by and move across water surfaces. Among the true bugs, the Gerridae (water strid-ers) and related families, the Veliidae (broad-shouldered water strid-ers) and Hydrometridae (water measurers), are able to skate across the water. Adaptations for this habit include retractable preapical claws to assist in swimming, elongate legs and body to distribute the insect’s weight over a large area of the surface film, and hydrofuge (nonwetta-ble) hairpiles for support on the surface. Some gerrids also are capable of detecting surface vibrations caused by potential prey. Adult whirligig beetles (Gyrinidae) live half in and half out of water with each eye divided into upper and lower halves, permitting vision simultaneously in both the air and the water; glands keep the upper portion of the body greased to repel water. The middle and hind legs of adult gyrinids are paddle shaped, enabling them to be one of the most effective swimming invertebrates. Among the Diptera, only the mosquitoes (Culicidae) may be considered to be permanent members of the pleuston of len-tic waters. The larvae and pupae of most species use the underside of the surface film for support. Larval Anopheles lie horizontally immediately beneath the air-water interface, supported by tufts of float hairs on each. Larvae of most other genera (Aedes, Culex, Culiseta) hang upside down, with an elongated terminal respiratory siphon penetrating the surface film. Feeding adaptations associated with pleuston specialization include predation by the Hemiptera and Coleoptera, to practically all functional feeding modes by different mosquito larvae, including coUecting-filtering and gathering, scraping, and shredding (Table IV).

The Nekton and Plankton Communities

The nekton are swimmers able to navigate at will (e.g., Coleoptera, Hemiptera, some Ephemeroptera), whereas plankton are floating organisms whose horizontal movements are largely dependent on water currents. The phantom midge Chaoborus sp. (Chaoboridae) (Fig. 3A) is normally regarded as the only planktonic insect and is abundant in many eutrophic (nutrient-rich) ponds and lakes. The tra-cheal system in these larvae is reduced to kidney-shaped air sacs that function solely as hydrostatic organs, and the larvae slowly descend or rise by adjusting the volume of the air sacs. Chaoborus remains in ben-thic regions during the day but moves vertically into the water column at night. These journeys are dependent on light and oxygen concentrations of the water. The larvae avoid predation by being almost transparent, and they have prehensile antennae that are used as accessory mouthparts to impale zooplankton (Fig. 3A). The only other group of insects that may be considered to be planktonic are the early chirono-mid instars, which have been reported in the open-water column.
Among the Heteroptera, nektonic species are in the Notonectidae (back swimmers), Corixidae (water boatman), and Belostomatidae (giant water bugs), all of which are strong swimmers. Many of these rise to the water surface unless continuously swimming or clinging to underwater plants. Notonectids have backs formed like the bottom of a boat and navigate upside down. They hang head downward from the surface or dive swiftly, using their long hind legs as oars. On the underside of the body, they carry a silvery film of air, which can be renewed at regular intervals, for breathing while submerged. Two genera of back-swimmers (Anisops and Buenoa) use hemoglobin for buoyancy control, and this adaptation has enabled these insects to exploit the limnetic zone of fishless lentic waters, where they prey on small arthropods.
They have been considered for use as biological control agents for mosquito larvae in some areas of North America. In contrast to notonectids, corixids always swim with the back up, using their elongate, flattened oarlike legs. Although some water boatmen are predators, they are the only group of semiaquatic Heteroptera that have members that are collectors, feeding on detritus and associated small plant material. The Belostomatidae are strong swimmers, but probably spend most of their time clinging to vegetation while awaiting prey, rather than actively pursuing their food in the open water. They are masters of their environment and capture and feed on a variety of insects, tadpoles, fish, and even small birds. The eggs of many belostomatids are glued to the backs of the males by the females and carried in this position until nymphs emerge, a remarkable adaptation for protection of the eggs.
Although most aquatic beetles (Coleoptera) are associated with the substrate, members of the Dytiscidae (predaceous diving beetles) and the Hydrophilidae (water scavenger beetles) are often found swimming in the water column and together constitute the majority of all species of water beetles. The dytiscids are mainly predators in both the adult and larval stage (Fig. 3C and 3D), while adult hydrophilids are omnivorous, consuming both living and dead materials. The larvae of hydrophilids are predaceous (Fig. 4A). To respire, hydrophilid adults, having their largest spiracles on the thorax, break the surface film with their antennae; dytiscids, having their largest spiracles on the abdomen, come up tail end first, as do the larvae of both families. Overall, there are actually few truly nektonic insects, and most of them pass through the limnetic zone when surfacing for emergence. This may be, partly, because with no resting supports in the limnetic zone, maintaining position requires continuous swimming or neutral buoyancy. The vast majority of lentic insects occur in shallow water with emergent plants and are considered to be part of the benthos.

The Benthos Community

Benthos, derived from the Greek word for bottom, refers to the fauna associated with the solid-water interface and includes insects residing on the bottom or associated with plant surfaces, logs, rocks, and other solid substrates. In lentic habitats, many insects fall into this category as mentioned earlier, particularly the Chironomidae, which often represent over 90% of the fauna in the profundal (deep-water) zone of lakes and ponds. These inhabitants are mostly bur-rowers that feed on suspended or sedimented organic materials and are capable of tolerating low dissolved oxygen or even anaerobic conditions. Chironomid larvae build U- or J-shaped tubes with both openings at the mud-water interface. Body undulations cause a current of water, providing conditions under which oxygen and particu-late food can be drawn through the tube. Some midge larvae found in sediments (mainly Chironomus sp.) are bright red and are known as bloodworms (Fig. 4B). The red color is caused by the respiratory pigment hemoglobin, which enables a larva to recover rapidly from anaerobic periods because the pigment takes up oxygen and passes it to the tissues more quickly than is possible by diffusion alone.
Other members of the benthos of deeper waters include the mayfly, Hexagenia (Ephemeridae), which inhabits the silt and mud of nearshore lake bottoms and has legs modified for digging to construct U-shaped burrows (Fig. 2B ) . Mayfly numbers have been increasing because of improved water quality standards for lakes and streams. Exceptions to the main constituents of the profundal zone are some immature mayflies, stoneflies, and caddisflies that have been collected at depths from 30 to 100 m in Lake Superior, Michigan. Also, a stonefly, Utacapnia lacustra (Capniidae), occurs at depths of 80 m in Lake Tahoe, California-Nevada, and completes its entire life cycle at this depth, never needing to surface.
Several orders of aquatic insects reach their greatest abundance and diversity in the shallow littoral zone of ponds and lakes as benthos typically associated with macrophytes (macroalgae and rooted vascular plants). The occupants are burrowers, climbers, sprawlers, clingers, swimmers, and divers (Table III) and include the Ephemeroptera, Heteroptera, Odonata, Trichoptera, Megaloptera, Lepidoptera, Coleoptera, and Diptera. The same groups occupy marshes and some swamps, which generally tend to be shallow, with an associated plant zone across the entire surface. Mayflies belonging to the families Baetidae and Siphlonuridae are generally swimmers, clingers, and climbers in vegetated ponds and marshes and mainly feed by means of collecting-filtering or -gathering (Table IV). Heteroptera include the water scorpions (Nepidae), which have long slender respiratory filaments and are well concealed by detritus and tangled plant growth because of their sticklike appearance. These sit-and-wait predators capture organisms that frequent their place of concealment. Other families of Heteroptera adapted for moving through vegetation in ponds are the Pleidae or pygmy backswimmers and creeping water bugs, the Naucoridae.
The Odonata, particularly the Gomphidae, are all predators and usually conceal themselves by either burrowing in substrate, sprawling among fine sediment and detritus, or climbing on vascular plants. Sprawlers are more active hunters and include the Libellulidae (Fig. 4C) and Corduliidae. Numerous setae give them a hairy appearance to help camouflage the larvae, and color is protective in patterns of mottled greens and browns. Most Zygoptera (damselflies) and the dragonfly (Anisoptera) family Aeshnidae are mainly climbers or cling-ers, lurking in vegetation or resting on stems of aquatic plants. The larvae stalk their prey, and both dragonfly and damselfly larvae have a unique lower lip (the labium) armed with hooks, spines, teeth, and raptorial setae that can extend to seize prey and then bring it back into the mouth, holding the food while it is being eaten. The food of larval odonates consists of other aquatic insects such as midges, semiaquatic bugs, and beetles, as well as small fish. Predators of larval odonates include aquatic birds, fish, and large predaceous insects.
In the order Megaloptera, which includes the hellgrammites or dobsonfly larvae of streams, only the predaceous larvae of the alder-fly (Sialis) is common in ponds and lakes. They are generally found in sand or mud along the margins, but occasionally in deeper water, and they prey on insect larvae and other small animals. The only aquatic family in the related order Neuroptera is the Sisyridae (the spongilla flies), and these are found feeding on freshwater sponges that occur in some streams and the littoral zones of lakes and ponds. The larvae, which occur on the surface or in the cavities of the host, pierce the sponge cells and suck the fluids with their elongated mouthparts.
Although most caddisflies are observed living in lotic waters, several families of caddisflies are either associated with temporary ponds in the spring, aquatic vegetation in permanent ponds, lakes and marshes, or wave-swept shorelines of lakes. The Hydropsychidae (net spinners), Helicopsychidae (snail case makers), Molannidae, and Leptoceridae are often found along wave-swept shorelines of lakes, and their feeding habits range from those of scrapers and collector-filterers to predators. The Phryganeidae and several genera within the Limnephilidae are climbers, clingers, and/or sprawlers among vegetation in temporary and permanent ponds and marshes; generally, they are shredders of vascular hydrophytes and other decaying plants. The cases of lentic caddisfly families vary with the environment they are found in. Some cases consist of narrow strips of leaves put together in spiral form around a cylinder (Phryganeidae: Phryganea sp.), others consist of plant materials such as leaves and bark arranged transversely to produce a bulky cylindrical case (Limnephilidae: Limnephilus) ( Fig. 3B ).
Both aquatic and semiaquatic moths (Lepidoptera) occur in len-tic habitats, and several genera form close associations with vascular hydrophytes. Larvae of the family Pyralidae (Parapoynx sp.) spend the first two instars on the bottom and feed on submerged leaves of water lilies, whereas older larvae generally become surface feeders. Silk spun by the caterpillars is often used to build protective retreats, and pupation usually takes place in silken cocoons or silk-lined retreats. Larval habits of aquatic and semiaquatic moths include leaf mining, stem or root boring, foliage feeding, and feeding on flower or seed structures. One semiaquatic lepidopteran called the yellow water lily borer (the noctuid Bellura gortynoides), mines the leaves as a young caterpillar and then bores into the petioles of lilies as an older caterpillar. Within the petiole, larvae are submerged in water and must periodically back out to expose the posterior spiracles to the air before submerging again. The larvae swim to shore by undulating their bodies and overwinter under leaf litter in protected areas.
In addition to the water scavenger and predaceous diving beetles that may occur as nekton swimming through the water column, larvae and adults of other beetles are considered to be part of the benthos of ponds and marshes. These include the Haliplidae (crawling water beetles), which are clingers and climbers in vegetation, and the Staphylinidae (rove beetles), which are generally found along shorelines and beaches, as well as in the marine intertidal zone. The Scirtidae (marsh beetles) are generally found associated with vascular hydrophytes but also are a prominent inhabitant of tree holes. The aquatic Chrysomelidae (leaf beetles) occur commonly on emergent vegetation in ponds, especially floating water lily leaves. The larvae of one genus, Donacia, obtain air
from their host plant by inserting the sharp terminal modified spiracles into the plant tissue at the base of the plant. Water lilies can be heavily consumed by larvae and adults of the chrysomelid beetle, Galerucella sp., and some of the aquatic herbivorous beetles belonging to the family Curculionidae (weevils) include pests of economic importance such as the rice water weevil (the curculionid Lissorhoptrus).
The Diptera is clearly one of the most diverse aquatic insect orders, inhabiting nearly all lentic habitats and representing all functional feeding groups and modes of existence. Although the benthic Chironomidae may reach their highest densities in the profundal zone of eutrophic lakes and ponds, they also are largely represented in the littoral zone associated with submergent and emergent plants, where they often graze on the algae attached to leaf surfaces or are vascular plant miners. Other dipteran families that occur in the littoral or limnetic zone, along with their specific habitat, habit (mode of locomotion, attachment, or concealment), and functional feeding mode are summarized in Table V. Among these, a few are of particular interest because of their high diversity and/or abundance in these habitats, namely the crane flies (Tipulidae), the shore and brine flies (Ephydridae), and the marsh flies (Sciomyzidae). The Tipulidae, the largest family of Diptera, are found along the margins of ponds and lakes, freshwater and brackish marshes, and standing waters in tree holes. A few littoral species inhabit the marine intertidal zone. To these are added the large numbers of species that are semiaquatic, spending their larval life in saturated plant debris, mud, or sand near the water’s edge or in wet to saturated mosses and submerged, decayed wood. Ephydridae larvae have aquatic and semiaquatic members and occupy several different


Summary of Ecological Data for Benthic Aquatic and Semiaquatic Diptera Larvae Inhabiting Lentic Habitats

Family Habitat Habit Functional feeding mode
Ceratopogonidae (biting midges, “no-see-ums”) Littoral zone (including tree holes and small temporary ponds and pools) Generally sprawlers, burrowers or planktonic (swimmers) Generally predators some collector-gatherers
Chironomidae (nonbiting midges) All lentic habitats including marine, springs, tree holes Generally burrowers, sprawlers most are tube builders); some climber-clingers Generally collector-gatherers, collector-filterers; some shredders and scrapers
Corethrellidae Limnetic and littoral margins Sprawlers Predators
Psychodidae (moth flies) Littoral detritus (including tree holes) Burrowers Collector-gatherers
Ptycopteridae (phantom crane flies) Vascular hydrophytes (emergent zone), bogs Burrowers Collector-gatherers
Tipulidae (crane flies) Littoral margins, floodplains (organic sediment) Burrowers and sprawlers Generally shredders, collector-gatherers
Dolichopodidae Littoral margins, estuaries, beach zones Sprawlers, burrowers Predators
Stratiomyidae (soldier flies) Littoral vascular hydrophytes; beaches (saline pools, margins) Sprawlers Collector-gatherers
Tabanidae (horseflies, deerflies) Littoral (margins, sediments and detritus); beaches, marine and estuary Sprawlers, burrowers Predators
Canacidae (beach flies) Beaches — marine intertidal Burrowers Scrapers
Ephydridae (shore and brine flies) Littoral (margins and vascular hydrophytes) Burrowers, sprawlers Collector-gatherers, shredders, herbivores (miners), scrapers, predators
Muscidae Littoral Sprawlers Predators
Scathophagidae (dung flies) Vascular hydrophytes (emergent zone) Burrower-miners (in plant stems), sprawlers Shredders
Sciomyzidae (marsh flies) Littoral—vascular hydrophytes (emergent zone) Burrowers, inside snails Predators or parasites
Syrphidae (flower flies) Littoral (sediments and detritus), tree holes Burrowers Collector-gatherers

lentic habitats ranging from saltwater or alka line pools, springs, and lakes to burrowers and miners of a variety of aquatic plants in the littoral margins of these freshwater lentic habitats. All larvae utilize a variety of food, but algae and diatoms are of particular importance in their diet. The Sciomyzidae share some of the same habitat with the shore and brine flies, particularly fresh- and saltwater marshes, and along margins of ponds and lakes among vegetation and debris. The unique aspect of their larval life is that they are predators on snails, snail eggs, slugs, and fingernail clams. The aquatic predators float below the surface film and maintain buoyancy by frequently surfacing and swallowing an air bubble. Prey may be killed immediately or over a few days.


As noted earlier, insects have been largely unsuccessful in colonizing the open ocean, except for some members of the heterop-teran family Gerridae. Most marine insects live in the intertidal zone (i.e., between high and low tide marks), especially on rocky shores or associated with decaying seaweed on sandy beaches (Table I) . Although several orders have representatives in the intertidal zone, only a few orders, notably the Diptera, Coleoptera, and Collembola, have colonized these habitats in any numbers. The harsh physical environment of this area has forced these groups to occur buried in sand or mud and to hide in rock crevices or under seaweed.


Because of adaptive radiation over evolutionary time, insects have colonized virtually every aquatic habitat on earth. Therefore, it is not surprising that these organisms are found in the most unusual of aquatic habitats. The title of most versatile aquatic insect must be shared among members of the dipteran family Ephydridae, or shore flies. Shore flies can breed in pools of crude petroleum and waste oil, where the larva feed on insects that become trapped on the surface film. Other species of this family (Ephydra cinera), known as brine flies, occur in the Great Salt Lake, Utah, which has a salinity six times greater than that of seawater. Larvae maintain water and salt balance by drinking the saline medium and excreting rectal fluid that is more than 20% salt. Another related family of flies, the Syrphidae, or “rat-tailed maggots,” occur in sewage treatment lagoons and on moist substrates of trickling filter treatment facilities. Both families have larvae with breathing tubes on the terminal end, which permits the larvae to maintain contact with the air while in their environment. Some Stratiomyidae, or soldier flies, live in the thermal hot springs of Yellowstone National Park with temperatures as high as 47°C! Other members of this family inhabit the semiaquatic medium of cow dung and dead corpses. A few species of insects have invaded caves and associated subterranean habitats, as mentioned earlier (see Lotic Habitats).
Another unusual aquatic habitat that several insect orders occupy is referred to phytotelmata or natural container habitats and include tree holes, pitcher plants, bromeliads, inflorescences, and bamboo stems. Synthetic container habitats, such as old tires, cemetery urns, rain gutters, and similar natural habitats such as hoofprints also harbor similar insects. Some of these habitats are extremely small and hold water only temporarily, but nevertheless can be quite diverse. The most common order found in these habitats is the Diptera with more than 20 families reported. Over 400 species of mosquitoes in 15 genera alone inhabit these bodies of water and some of these species are important vectors of disease agents.
Insect communities inhabiting pitcher plants (Sarracenia purpurea) in North America are exemplified by a sarcophagid or flesh fly (Blaesoxipha fletcheri), a mosquito (Wyeomyia smithii), and a midge (Metriocnemus knabi). The relative abundance of these pitcher plant inhabitants is related to the age, inasmuch as each of the three species consumes insect remains that are in different stages of decomposition. Specifically, the larvae of the flesh fly feed on freshly caught prey floating on the pitcher fluid surface. The mosquito larvae filter feed on the decomposed material in the water column, and the midge larvae feed on the remains that collect on the bottom of the pitcher chamber. Temporary habitats are important because they are populated by a variety of species, often with unique morphological, behavioral, and physiological properties.

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