The name “dobsonflies” confuses many people. These large insects are not really flies at all. They are members of the order that includes lacewings and antlions.
Dobsonflies are very large insects. Their wings and mouthparts make them look even larger than they really are. They have very large wings that fold on top of the body when they are resting.
Male dobsonflies have very large mandibles. They extend almost an inch from the front of the head. A male dobsonfly can reach more than 4″ in length from the tip of the wings to the tip of its mandibles.
If they are threatened, male dobsonflies open their mandibles as if to bite. They do not actually bite because their mandibles are too awkward. Females have shorter mandibles and they can deliver a painful bite. They do not inject venom, however both males and females can produce an unpleasant-smelling fluid that they use as defense.
Dobsonflies are most common around streams. They deposit their eggs near the water or on vegetation that hangs over the water. When the eggs hatch, the larvae move into the water.
Dobsonfly larvae are called hellgrammites or dobsons. They live under stones in the stream. They prey on other larvae and small animals. They have pincers on their head and a distinctive segmented body. They can grow to almost 3″ in length.
People often catch hellgrammites to use as fishing bait. Many people use nets across the stream to catch the hellgrammites. However, some people simply put their hands under stones until a hellgrammite attacks their finger.
After the larvae are fully-grown, they make a cocoon where they change into adult dobsonflies. After they emerge, the adults are active at night around the stream where they developed. They are attracted to lights and they can sometimes become a nuisance around homes near the stream. Adult dobsonflies only live a few days while they produce their eggs.