Science of Water : Concepts and Applications

Water Ecology 195
They push their mouths into the prey, paralyze it, and suck the insect dry. Predators of the water
strider, such as birds, fi sh, water beetles, backswimmers, dragonfl ies, and spiders, take advantage of
the fact that water striders cannot detect motion above or below the water’s surface.
(7) ALDERFLIES AND DOBSONFLIES (ORDER: MEGALOPTERA)
Larvae of all species of Megaloptera (“large wing”) are aquatic and attain the largest size of all
aquatic insects. Megaloptera is a medium-sized order with less than 5000 species worldwide. Most
species are terrestrial; in North America 64 aquatic species occur.
In running waters, alderfl ies (Family: Sialidae) and dobsonfl ies (Family: Corydalidae; sometimes
called hellgrammites or toe biters) are particularly important. They are voracious predators,
having large mandibles with sharp teeth.
Alderfl y brownish-colored larvae possess a single tail fi lament with distinct hairs. The body
is thick-skinned with six to eight fi laments on each side of the abdomen; gills are located near
the base of each fi lament. Mature body size is 0.5–1.25 in. (see Figure 6.29). Larvae are aggressive
predators, feeding on other adult aquatic macroinvertebrates (they swallow their prey without
chewing); as secondary consumers, other larger predators eat them. Female alderfl ies deposit eggs
on vegetation that overhangs water, and the larvae hatch and fall directly into water (i.e., into quiet
but moving water). Adult alderfl ies are dark with long wings folded back over the body; they only
live a few days.
Dobsonfl y larvae are extremely ugly (thus, they are rather easy to identify) and can be rather large,
anywhere from 25 to 90 mm (1–3 in.) in length. The body is stout, with eight pairs of appendages
on the abdomen. Brush-like gills at the base of each appendage look like “hairy armpits” (see
Figure 6.30). The elongated body has spiracles (spines) and three pair of walking legs near the
upper body and one pair of hooked legs at the rear. The head bears four segmented antennae, small
compound eyes, and strong mouth parts (large chewing pinchers). Coloration varies from yellowish
to brown, gray and black, often mottled. Dobsonfl y larvae, commonly known as hellgrammites, are
usually found along stream banks under and between stones. As indicated by the mouthparts, they
are predators and feed on all kinds of aquatic organisms. They are an important food source for
larger game fi sh.
FIGURE 6.29 Alderfl y larvae.
FIGURE 6.30 Dobsonfl y larvae.