Midsummer is the time of year when human encounters with an insect known as a dobsonfly are likely to occur. Such encounters are rare, but when they happen, most humans react as if they have just come face to face with some prehistoric monster from the Black Lagoon. And in a sense, they have.
Dobsonflies are sometimes classified as Megaloptera, and fossil Megaloptera have been discovered dating to the Lower Permian period some 270 million years ago. The name Megaloptera is based on the fact that these insects have wings that are large relative to their body size.
Some scientists classify dobsonflies in the insect order Neuroptera. The name is appropriate for these insects because the veins in their wings form a pattern that suggests a series of nerves. Insects called lacewings, commonly found in our gardens, are also classified as Neuroptera.
Both dobsonflies and lacewings have soft bodies and membranous wings, with many cross veins. These are predatory insects that possess biting mouthparts. One of the major differences between the lacewings and the dobsonflies is size. Lacewings are fairly small insects, while dobsonflies include some of the largest insects found in North America.
One of the more common dobsonflies is Corydalis cornuta with a wingspan of more than five inches. Dobsonflies and the lacewings are not good flyers, in spite of their large wings. Flight of these insects is suggestive of a human learning to swim: a lot of thrashing of arms and legs and not much forward motion.
Exactly why dobsonflies have this common name is obscure. In his 1897 book Insect Life, John Henry Comstock referred to this insect as the dobson or horned corydalis. The latter name is based on the genus name assigned to the insect by Carl Linnaeus – the most prolific scientific namer of living things in history – and the fact it has long antennae, which are sometimes called horns.
According to Comstock, anglers collected the aquatic larva of the dobsonfly to use as fishing bait and referred to the insect as "the dobson." It is probably the case that the human surname Dobson was the inspiration for the common name of the insect. Exactly who Dobson was and why his or her name was used for this insect larva are unknown.
Comstock also reported that anglers sometimes called the larva of this insect a hellgrammite. The origin of the term hellgrammite is also obscure. However, Comstock says it is "an ugly creature" and is used for fish bait, "in spite of its disagreeable appearance." Such a description might indicate that the inclusion of "hell" in the name is appropriate.
Hellgrammites are popular bait for fishing, especially for bass and trout. Lures constructed to resemble this creature can be purchased at many sporting goods stores. However, some anglers prefer to use live hellgrammites. That involves collecting the bait. Entomologist Comstock suggested collection could be accomplished by placing a net or wire screen down-current from stones in a stream. When the stones are lifted with a rake, the hiding hellgrammites would be dislodged and captured in the net.
The life cycle of the dobsonfly goes like this. Hellgrammites spend three years in the water, where they prey on other aquatic insects. When full grown, the hellgrammite will crawl from the water in May or June and form a cell in the soil. It changes into a pupa in the earthen cell, and a month or so later emerges as the adult. Female adults deposit eggs on objects adjacent to water. When the eggs hatch, the larvae enter the water, and the cycle begins again.
Adult dobsonflies are sometimes attracted to light during nighttime hours. That often leads to humans discovering them as they flutter around or cling to a surface near a light. The male has long mandibles that strike fear into the people who see them. However, they cannot bite with those mandibles. On the other hand, mandibles of the females are short and can inflict a painful bite.
And that friends, once again supports the ancient idea that in the insect world, it is the female that bites and stings while the male just looks mean!