This week’s show is dedicated to WERU’s own News Editor, Amy
Browne. I happen to know, from social media, just how she feels about the
animal we are going to talk about today, though I also know from experience,
she’s not alone.
The animal, the bane of existence for so many people, and so
many companion animals this time of year, is the deer fly. The common name Deer
fly refers to a group of animals in the genus Chrysops, of which there are
about 100 species in North America alone. Deer flies are in the insect order
Diptera, with all the other flies, in this case their common name is not a
trick. It is the females that cause us so much grief. They require a blood meal
from a vertebrate to ensure viability of their eggs. Males sip nectar from
flowers, (like male mosquitos) for their sustenance. Deer flies (and their
closely related bretheren Horse flies) are universally referred to in the
literature as having “knife like” mouth parts. They achieve the required blood
meal by slashing away at the flesh of the victim, causing a generalized
bleeding, which they then slop up with their “sponge like” mouth parts. This
part of the story you know well, if you spend any time outside in Maine in the
summer.
I wanted to know more about these extremely annoying
creatures, so I dug in a bit to see what I could find. And it turns out it is
much as I suspected. They are hydrobionts, meaning they need wet areas in which
to breed. The females, after their blood meal, lay their eggs on the underside
of leaves in the understory or in swamp areas, above damp or wet ground. When
the eggs hatch the larvae that emerge drop into the wet ground below and burrow
in, living on detritus or as predators of smaller insects and worms. The larvae
are active all winter, below the frost line apparently, and after feeding all
winter they apparently pupate in early spring for a few weeks. The adults
emerge in summer and live from one to two months, tormenting me and Amy Browne
and our dogs, and anyone else foolish enough to be outside in wet areas when
the temperature is warm enough. One of the sources I found indicated a minimum
temperature range of 72 degrees F, but I know that to be incorrect, at least
for the deer flies here in Maine. If I can get out before the temperature hits
60 degrees I know I will miss most of them, but above that, they are good to
go. They are also primarily visual predators, attracted first and foremost to
dark objects that move. If I wear a light colored shirt on my morning run I am
much less bothered. My large black thin coated dog however, has no such choice.
Sources say that scent and other biological cues like carbon dioxide are also
attractants, but my experience leads me to believe the idea that they are
primarily visual. It seems that their job in this world is to bite, and bite
well, much to our chagrin.
Isn’t that the job of every animal? Every organism? To do
whatever it can to carry on and pass on its genes? It is easy to disparage a
biting insect that bothers us for one to two months a year, but we have to
remember that everything has a job in an ecosystem. The job of many of the deer
fly eggs is to get parasitized by wasps. The job of many deer fly larvae is to
get invaded by bacteria and fungus and other microbial parasites. The job of
many an adult deer fly is to get eaten by swallows and flycatchers and
predatory insects like dragon flies and hornets. The job of the ones that
survive is to reproduce, and to do that, they need us, or our dogs, or our
livestock, or more likely, the large vertebrates that populate the north woods.
No body likes hanging out with deer flies. But all the same,
I prefer a world where they exist, a world as full as it can be with as many
different kinds of organisms as possible, a world rich and damp and squirming
with life. That is truly the point of it all, and we can’t do it without the
biters and scratcher anymore than we can do without the cute furry babies and
the fluffy little birds. They all count, every last knife like mouthpart
wielding one.
References:
More good stuff from Bug Guide: http://bugguide.net/node/view/11387/bgpage
Here’s a whole bulletin about them from the Maine Forest
Service: http://library.umaine.edu/MaineAES/TechnicalBulletin/tb160.pdf
