This is the time of year when people notice one of the largest insects in Iowa, the dobsonfly (Corydalus spp., Megaloptera: Corydalidae). These large prehistoric-looking creatures measure two to four inches from the front of the head to the wing tips. They originate in rivers and streams but can also be found in town.. They are soft-bodied and brownish-gray with the wings held roof like over the body. The wings have a large number of veins (lines) and are often mottled. The antennae are long and threadlike. A distinguishing characteristic is the mandibles. Males have long, curved, sickle-shaped mandibles approximately 1 inch in length. The females have shorter less conspicuous jaws. See the photo below.
Dobsonflies are active at night and are attracted to lights. They have an awkward fluttery flight but still travel considerable distances and are occasionally found some distance from a body of water. Adults live for a brief period and do not feed. Dobsonflies develop from underwater larvae known as hellgrammites. The larvae live for up to three years among rocks on the bottom of flowing rivers and streams where they feed on insects and small fish. They typically occur only in high quality, well-oxygenated water. Larvae grow up to three inches in length are dull colored and have gill filaments and feathery gill clusters along the sides of the abdomen.
Dobsonflies are harmless to property and crops. No control treatments are necessary. Though they don't feed on people, both adults and larvae will bite if handled carelessly.