Fishflies Dobsonflies and Alderflies: Megaloptera

Adult alderflies measure 0.4 to 0.6 inches (10 to15 millimeters) in length, while dobsonflies and fishflies are 0.6 to 2.4 inches (40 to 75 millimeters). They are soft-bodied insects and are black, brown, or yellowish orange to dark green. The head is broad and flat and has chewing mouthparts that are directed forward. The antennae (an-TEH-nee), or sense organs, are long, feathery (fishflies), threadlike (dobsonflies), or beadlike (alderflies). Their compound eyes, or eyes with multiple lenses, are large. Only the dobsonflies and fishflies have simple eyes, or eyes with only one lens. The four wings of alderflies are held like a roof over the body when at rest, but those of dobsonflies and fishflies are kept flat. Megalopteran wings are membrane-like and have a complex network of veins that is not branched at the edges of the wings. The hind wings are broader than the forewings and are folded fanlike underneath them. The abdomen is ten-segmented and does not have any projections at the tip.

The larvae (LAR-vee), or young of animals, do not resemble the adults. Larvae of alderflies reach a maximum length of 1 inch (25 millimeters), while those of dobsonflies (known as hellgrammites) and fishflies measure 1.2 to 2.9 inches (30 to 65 millimeters). Their bodies are long and flat. The head is flat and has short antennae. The chewing mouthparts are directed forward. A hard, shieldlike plate covers each of the three segments of the thorax, or midsection. The first segment of the thorax is almost square in shape. The abdomen has seven or eight long slender abdominal gills on each side. The gills absorb oxygen from the water, allowing the larvae to breathe. In alderflies, the abdomen ends in a single, threadlike projection, but in dobsonflies and fishflies it ends in a pair of leglike structures, each with two hooklike claws.