Image of a female dobsonfly
Female dobsonfly

Description of dobsonflies  

The dobsonfly (Corydalus, spp., Neuroptera: Corydalidae) is 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. They are soft-bodied and brownish-gray with the wings held rooflike over the body. The wings have a large number of veins (lines) and are often mottled. The antennae are long and threadlike. Males have long, curved, sickle-shaped mandibles (jaws) approximately 1 inch in length. The females have short inconspicuous jaws.

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.

Damage caused by dobsonflies 

Dobsonflies found in unsuspected locations away from the river can be safely ignored. Handling dobsonflies is only somewhat risky. It is the female with the short, inconspicuous mandibles that can inflict the more painful bite if handled carelessly. No control treatments are necessary.

Image of a male dobsonfly
Male dobsonfly 

Life cycle of  dobsonflies  

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 an excellent fish bait. Larvae can inflict a painful bite when mishandled.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.  

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 12, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.