Eastern Dobsonflies (Corydalus cornutus)
look like something out of someones nightmare. They are large,
alien-looking, and downright intimidating in their appearance. They
measure well over three inches in length and with those sickle-like
mandibles, the males are often 4 inches or more. Females lack the longer
mandibles, but possess a painful bite when harassed. The larger
mandibles of the male lack bite force and are most likely used to
impress the ladies or to fight off potential competition from rival
males. Some resources claim the males use those mandibles to flip rival
males onto their back in a form of combat to win the affection of a
nearby female. Apparently these WWE
wrestling matches between males weed out the weaker individuals and the
stronger, more capable males will mate and have their genetics carried
into the next generation.
After mating, females will
form egg masses on vegetation near a water source, usually a moving
stream or small river. These egg masses are often clustered together as
several females will use the same location to lay their eggs, in a type
of Dobsonfly rookery. The eggs hatch and the nymphs, called Hellgrammites
must find their way to water. Whether they just gracefully fall into
the water or crawl their way there is dependent upon how far away from
the water the egg mass was formed. Often this can be quite a distance,
so dropping into the water would not be an option for those individuals,
instead they will have to hoof it to the nearest water source and hope
hungry predators don't find them along the way. Once in the water the
little Hellgrammites
will look for suitable places to hide. Typically this will be under
stones and other debris on the bottom of the stream. They lurk about
waiting for aquatic insects to come within grabbing range and they will
pounce and slink back into the dark recesses of their burrow. With a
name like Hellgrammite,
it calls to mind images of some great Hell-beast lurking in the depths
below the waters surface waiting to wreck havoc. If you are a small
aquatic insect these larvae are indeed a beast to be reckoned with,
however for humans you've nothing to fear except a resounding pinch from
their strong mandibles should you grab one. I found one in the flood
waters of the Nodaway
River one spring. I had no idea what it was as I watched it wiggle and
attempt to swim through the shallow waters covering a county road near
the river. I have always been a "I need to touch it kinda person" and
this sometimes gets me into trouble. I very quickly realized my mistake
as the little bugger bit me resoundingly on the finger as soon as I
grabbed it. I dropped it in short order....lesson learned. It was at this point I recognized what it was and gained a healthy respect for them.
Fishermen have used Hellgrammites for hundreds of years as bait to catch trout and other game fish. Trout fisherman create very convincing flies that mimic hellgrammites much to the chagrin of a hungry trout. Many water creatures including salamanders, fish and crayfish all feed on hellgrammites, which might explain why they hide under stones and other debris.
Once Hellgrammites
have had time to grow and reach their full larval size, usually after
12 molts or skin sheds, they will leave the water and look for a place
on land to burrow into loose soil where they will create a pupal cell.
Once buried and safely ensconced in this chamber they will remain here
for 7 to 14 days as they pupate into adult Dobsonflies.
When the adults emerge they will begin looking for mates to pass on
their genetics to the next generation. Males live about three or four
days, females live up to ten days.
In Virginia and Pennsylvania the emergence of the Hellgrammites
from their watery homes seems to be synchronous. A mass exodus of these
little hell-beasts is usually triggered by a large thunderstorm; it is
believed that the vibrations of the thunder acts as some sort of signal
to the Hellgrammites
to leave the water and head for land. As the larvae crawl out of the
watery depths the locals call this phenomena "Hellgrammite Crawling,"
not to be mistaken for pub crawling.
It is uncommon
to find adults during the day as they hide out in vegetation near the
water. At night they are attracted to lights and are commonly found at
porch lights and other night time light sources. They have also been
found to be attracted to Mercaptan which is the substance that is added
to Natural gas and Propane that gives it the distinct odor we all
recognize as a potential leak. This apparent attraction they have to
this substance may act as a calling card to the presence of these
gasses. They also seem to prefer moderately clean water environments and
do not tolerate highly polluted water. This means they can be used as a
bio-indicator of potential health problems within watery habitats. If
these insects are present it is a good indication the water is healthy
and clean, if not, maybe these environments need a closer looking at.
There are 60 species of Dobsonflies in the order Megaloptera, which means "Large wing." Within this order there are 30 species in the genus Corydalus.
The Eastern Dobsonfly is the most common and largest within the United
States. They occur throughout Eastern North America from Canada to
Mexico. There are three species in the Western United States, however
the majority of species within this genus occur in South America.
What an amazing creature to find
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