Dobson Flies

Eastern Dobsonfly- fcps.edu

The chance finding of a male and female Dobsonfly attracted to our porch light gave us the opportunity to compare their anatomy in real time.  First a reminder that Dobsonflies, fishflies, dragonflies, etc are not true flies (i.e. Diptera).  You can tell the difference in the name- true flies are named in two words, i.e. house fly, fruit fly, etc.

Diptera have one set of wings while their second set of would-have-been wings have evolved into small antennae-like balancing structures called halteres.  Dobsonflies are in the Megaloptera order which includes fishflies and alderflies. All of these have four wings although you wouldn't know it from the usual pictures as they generally have them tucked tightly on their back.

Male Dobsonfly

Female Dobsonfly

These are Eastern Dobsonflies, Corydalus cornutus.  The male is a fearsome looking beast with long threatening jaws nearly half the length of its body.  Their threatening appearance makes one shy away from picking it up.  Actually the jaws are rather weak, used only for clasping a willing female to stay with him a little longer.  Measuring 2.25" long, it has an almost prehistoric appearance.

Female's Jaws

The female is the same size but has much smaller jaws.  Because this provides her much more mechanical leverage, she is able to transmit a painful bite.  This is one more reason to be very careful when dealing with the female of some species.

Adults only live 7 days and do not eat.  They live several years in the aquatic larval stage called hellgrammites.  They are a favored bait for fishermen although with increasing pollution they are harder to find in recent years. 

Videos are available at wn.com/DobsonFly and extensive scientific information is at tolweb.org/Corydalus.