Friday, August 8, 2014
Beloved Summer Insects: Deerflies
Note: This program first aired on August 2, 2014.
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.
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