Download Dobsonflies Look Vicious

Dobsonflies Look Vicious
08-08-13
AUGUST
2013
By
Tom Turpin
Professor of
Entomology
Purdue University
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Dobsonflies Look Vicious
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.
Female dobsonfly; photo by
John Obermeyer, Purdue
Extension
Dobsonflies are sometimes classified as
Megaloptera, and fossil Megaloptera have been discovered dating to
the Lower Permian period that existed 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 Male dobsonfly with long
than 5 inches. Dobsonflies and the
mandibles; photo by
lacewings are not good flyers, in spite of
John Obermeyer, Purdue
their large wings. Flight of these insects is Extension
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
Hellgrammite
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!
Writer: Tom Turpin
[email protected]
Editor: Olivia
Maddox
[email protected]