Animals - Freshwater Ecology: Concepts and Environmental Applications - page 169

ers. The net-spinning caddisflies use stream flow to filter organic materials
from the water column onto their nets. Adult caddisflies look like moths.
Although massive hatches can be a nuisance to humans, they signal anglers
that fish may be actively foraging.
The order Neuroptera (spongillaflies) used to include what is now con-
sidered a separate order, the Megaloptera (fishflies, dobsonflies, alderflies,
and hellgrammites). The megalopteran larvae have seven or eight pairs of
lateral filaments and large mandibles (Fig. 9.9G). They mostly occur in
cool, oxygen-rich waters but can be found in a variety of lentic and lotic
habitats. Some megaloptera larvae ( Corydalus, the hellgrammites) can be
more than 6 cm long and live for 2-5 years before emerging. Although
there are many families of terrestrial neuropterans, there are few aquatic
species. The name spongillaflies derives from their association with the
freshwater sponges on which they feed. All freshwater neuropterans and
megalopterans are predacious.
The order Heteroptera (which can also be considered a suborder of the
Hemiptera) includes the true bugs (Fig. 9.9J), most of which are terrestrial.
About one-third of the aquatic species live on the water surface and two-
thirds in the water. There are both lentic and lotic species. The true bugs
are distinguished by mouthparts modified to form a sucking and piercing
beak, a first pair of wings that are leathery at the base, a second pair en-
tirely membranous and simple, and gradual development to adult stages.
Most aquatic species are adapted for swimming (e.g., long, fringed setae
on their front legs) and breathing through siphons or taking air bubbles
under water with them to breath. The group includes the giant water bugs
(big enough to prey on small fish), the water boatmen (often seen in shal-
low littoral zones), and the gerrids (water striders).
Truly aquatic moth larvae (Lepidoptera) are few. The larvae of some
aquatic forms have numerous paired filamentous gills on the abdomen. Al-
though many species are found in ponds with dense macrophyte popula-
tions, others (e.g., Parargyractis ) can be abundant in streams and feed on
periphyton.
The Coleoptera (beetle) species with aquatic larval and/or adult stages
(Fig. 9.9D) represent only about 3% of this mostly terrestrial order. How-
ever, there are so many species of beetles in the world that they are signif-
icant components of the biodiversity of both lentic and lotic habitats. The
group includes the “riffle beetles” (Elmidae, with aquatic larvae and adults),
the “water pennies” (Psephenidae larvae, attached to rocks), the Gyrinidae
(whirligig beetles, with adults found on the surface), the predacious diving
beetles (Dytiscidae), and the water scavenger beetles (Hydrophilidae). Some
adult Coleoptera, along with some Hemiptera, transport air bubbles un-
derwater by means of specialized structures. Underwater, these air bubbles
can function as a physical gill, extracting O 2 from the surrounding water
through the bubble. The aquatic larvae of some Curculionidae and
Chrysomelidae are equipped with specialized spines that pierce plant tis-
sues and extract O 2 from submerged portions of emergent macrophytes.
Because of the many adaptations for using atmospheric O 2 , coleopterans
are often abundant and diverse in the poorly oxygenated waters of wet-
lands. Many coleopterans are important predators, whereas others are
adapted to scrape periphyton, graze aquatic plants, or utilize detritus.