Animals - Freshwater Ecology: Concepts and Environmental Applications - page 166

vegetation and catch adult aquatic insects. Spiders may be important con-
sumers of insects in riparian habitats and wetlands.

Subphylum Insecta and Collembola (Uniramia)
Ten insect orders contain aquatic species (Merritt and Cummins, 1995).
Insects are found in most freshwater habitats. They are probably the most
studied freshwater invertebrates. The majority of these species spend most
of their immature lives in the water, and the adults emerge from the aquatic
environment to mate and disperse. The insects have three major body re-
gions (head, thorax, and abdomen), one pair of antennae, compound eyes,
and specialized mouthparts. The thorax has three segments, each with a
pair of legs, and each leg is divided into five parts. The immature forms of
the aquatic insects are variously referred to as larvae, nymphs, or naiads .
The term larvae is more widely accepted by zoologists and is used in this
topic. Some characteristics of the aquatic orders of insects are summarized
in Table 9.2. Each of the orders will be discussed in turn.
The Collembola, or springtails, are not true insects. They are small,
eyeless and wingless arthropods (usually less than 6 mm long) that possess
a characteristic ventral tube (collophore) that functions in respiration and
osmoregulation and can also be adhesive (Fig. 9.9F). They differ from in-
sects by having only six abdominal segments and the mouthparts are with-
drawn into a pouch in the head capsule. Most species are terrestrial or
semiaquatic and occur in lentic habitats. Their biology and ecology in
freshwaters are not well-known.
Mayflies (Ephemeroptera) are often abundant as larvae in streams
(where they can provide an important food source for fish) and in the ben-

TABLE 9.2 Characteristics of Orders of Aquatic Insects and Collembola

Number of aquatic
and semiaquatic Functional

Order Common name species Habitats feeding groups

Collembola Springtails 50 Lentic, shallow Collectors

Ephemeroptera Mayflies 2,250 Lentic and lotic Scrapers, collectors,

few predators

Odonata Dragonflies and 5,500 Lentic and lotic Predators

damselflies

Plecoptera Stoneflies 2,140 Lentic mainly Shredders, collectors,

predators

Trichoptera Caddisflies 7,000 Lentic and lotic Predators, scrapers,

collectors

Megaloptera and Fishflies, alderflies, 300 Predators

Neuroptera and spongillaflies

Hemiptera Bugs 3,200 Lentic and lotic Predators

Lepidoptera Aquatic caterpillars 100 Lentic and lotic Shredders, scrapers

Coleoptera Water beetles 5,000 Lentic and lotic Predators, scrapers,

collectors, shredders

Diptera Flies and midges 30,000 Lentic and lotic Predators, scrapers,

collectors, shredders