Samples this week have included one of the largest insects in Iowa, the dobsonfly (Corydalus, spp., Neuroptera: Corydalidae). This is also one of the largest aquatic insects in North America. Adults measure two to four inches from the front of the head to the wing tips. Dobsonflies have a short, soft abdomen under their large, wrinkled, brownish-gray wings that are held rooflike over the body. The antennae are long and threadlike.

Enlarge	Dobsonfly near Evansdale, Iowa.
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The dominant feature of dobsonflies is the long, curved, sickle-shaped mandibles or jaws. Jaws of the males are especially obvious, mesuring approximately 1 inch in length but only one-eight inch in diameter. The females have short inconspicuous jaws only one-quarter inch long. Ironically the long male pincers are mostly ornamental and ineffective; the short female pincers can deliver a nasty pinch.

Dobsonflies are moderately common at Iowa rivers and streams though few people ever get to see them. They 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. Except for occasionally pinching careless handlers, dobsonflies are harmless and beneficial as a link in aquatic food chains.  Dobsonflies found in unsuspected locations away from the river can be safely ignored. No control treatments are necessary. 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 other small insects. 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. There are two hooks at the end of the abdomen. Hellgrammites are used occasionally as fish bait. Larvae can inflict a painful bite when mishandled.