Thursday, August 31, 2017

North Country Deerflies

deerfly My students and I were conducting research in the Winooski River floodplain at Saint Michael’s College last week when the buzzing became particularly intense. A brisk walk is enough to outdistance mosquitoes, but deerflies combine fighter jet speed with helicopter maneuverability. And a slap that might incapacitate a mosquito seems to have little effect on these relentless pests. Deerfly season 2017 started slowly, but by late July there were enough to carry off small children. On trails between wetlands and farm fields, we were dive-bombed by countless, persistent, little winged vampires. Insect repellent did little to repel them. We slapped, feinted, grabbed at thin air, and usually came up empty. It was like Caddyshack, but with flies rather than gophers.

The horsefly family Tabanidae includes deerflies, along with larger Alaskan “mooseflies,” and the greenheads that ruin many a trip to New England’s beaches. Iridescent green eyes that make up most of the fly’s head give them their common name. Far more impressive is their bite: they truly hurt. Because greenheads emerge only from saltmarshes, we know they travel up to two miles in search of blood.

Deerflies and their relatives risk getting hand-slapped and tail-flicked because humans and other mammals offer a high-protein food source they need to develop eggs. The gamble pays off; they are still here. Finding deerflies near water makes perfect sense, as ponds are especially important deerfly habitats. As is true for other tabanids, deerfly larvae prey on aquatic invertebrates. They complete their aquatic phase as pupae before emerging as adults.

Both genders consume nectar and pollen, but only the females enrich their diet with blood. Whether the males of the species lack initiative to bite mammals we can’t guess, but they certainly lack the equipment. The female’s sharp blade-like mouth parts inflict painful wounds that make mosquito bites look genteel.

Biting flies elicit questions like: What good are they? Or more thoughtfully, what is their role in nature? And also, could we get rid of just this one species? The disconcerting answer to the latter question is yes; molecular biologists have discovered how to eliminate a species by inserting harmful genes that can be spread through an entire population. Although we have accidentally driven many species extinct, to my knowledge, the only deliberate extinction thus far has been smallpox.

Having discussed the important role that insects play in an ecosystem’s food web and satisfied ourselves that driving deerflies from the planet was beyond our purview, my students and I resorted to a more local and fiendishly satisfying solution. We bought deerfly patches: double-sided sticky pads worn on our hats. When deerflies choose one of us as their next meal ticket they search for exposed skin. Does a deerfly patch looks like human skin? You’ll have to ask a deerfly. I won’t question why they land on the patch, but I will take this opportunity to thank each and every one of them that takes that one-way trip and ceases orbiting my head.

To test drive the patch I parked near a campus pond. A deerfly landed on the side mirror – game on! Typically, I’d be swarmed in the field and at least one deerfly ‘guest’ would join me for the car ride home. But this day would not be typical. I came forearmed. I had read the reviews; gawked in amazement at the online photographs of patches coated with innumerable flies stuck like so many direwolves in a tarpit.

I emerged from the car, hat and patch on head, and took a 15-minute walk between several ponds. During my walk I received one deerfly bite and swept another off my neck. I felt the familiar thuds of flies hitting my hat, but less orbital annoyance, it seemed to me. Wishful thinking? Time would tell.

The moment of truth: safely in my metal and glass cocoon, I removed the hat. Sure enough, the patch was emblazoned with 15 deerflies, a single stray mosquito … and no gophers. I rarely endorse products, and indeed a good friend tells me that a loop of duct tape is just as good. Whatever solution you choose, at least deerflies need not force you to choose the indoors.

Declan McCabe teaches biology at Saint Michael’s College. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine, and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation.


Guest Contributor

The Adirondack Almanack publishes occasional guest essays from Adirondack residents, visitors, and those with a biding interest in the Adirondack Park.

Submissions should be directed to Almanack editor John Warren at adkalmanack@gmail.com.




10 Responses

  1. drdirt says:

    Wow, I never heard of the patch ,.,, those deerflies can really annoy a hiker or paddler.

    Think I’ll try the duct tape on hat .,.,., hope I don’t catch any wooly algadids.

  2. Evelyn Greene Evelyn Greene says:

    There are other tricks too if you are short of sticky stuff. Walk with a dark dog in front of you and most deer flies (two words because they are real flies, not like dragonflies) will hang around it. Or carry a dark hat on top of a long stick and they will follow the highest dark moving thing. Wide-brimmed boat hats are also a help as the flies don’t like the dark shade and tend to move out without biting.

  3. Tom Vawter says:

    As a younger field biologist working on butterflies, I spent many hours plagued by deer flies. I never entirely avoided getting bitten, but I got great satisfaction from a defensive technique I developed using my large “professional” insect net. As Imwalked the fields, I’d continuously wave the net around my head in a figure-eight pattern. Occasionally I’d stop and check the net, which, on a good day, might contain 10 or 15 deer flies. Then I’d draw the net through my fingers, crushing all the flies in the process. I’m not sure it really helped
    In my defense, but the revenge was sweet.

  4. Richard L. Daly says:

    Deerflies? 1987, Rodeo – back when it was still PRCA-sanctioned, at Painted Pony Ranch in Lake Luzerne NY: Mom (+r.i.p.) and the rest of us enjoyed the show and our overinight stay
    in the (only room left) bunkhouse.Only she woke up with swollen lower legs that had been exposed during the arena event. Dr at cvph ER in Plattsburgh recognized the bite … She was treated topically and internally and survived to recall the wonderful outing. Let’s be careful out there, Rodeo Fans!

  5. geogymn says:

    I am fortunate as I don’t have a problem finding taller people to hike with.

  6. Stephen Daniels says:

    One trick that works exceedingly well for me while hiking, is to cut a small live branch from a shrub and carry it with the foliage draped over my head. It seems to confuse them, and no swarming.

    The other is to use the repellent Ole Time Woodsman, which contains pine tar. Deer flies will NOT swarm around you at all with this on.

  7. Scorr says:

    Just wear a hat with a full around brim like a cowboy hat. They make them for hikers too. I hope you cut live branches from your own property and not from someone else’s land and not from state lands.

    • Stephen Daniels says:

      Yes, I prune to the branch collar a small branch from a shrub on state land. Considering all the pruning from all the flying lead from hunters, the damage from recreation vehicles and hikers, the damage from insects and disease, the damage from extreme weather, the natural pruning process the plants undergo during their lifespans due to low light levels, I figure in the grand scheme of things, the loss of one small branch from a tree or shrub is not going to imperil the ecosystem. You may think differently.

      • Scott says:

        Stephen – You’re correct that you cutting one branch from a state land tree each time deer flies are out will not likely cause much harm. However, cutting state land trees is illegal and cutting someone else’s trees is just wrong even if they hadn’t made a law saying so. All the other activities you listed as quasi justifications don’t cut it.

    • JohnL says:

      Can’t speak to Adirondack deer flies but St Lawrence River deer flies will not bite if you have a hat with a brim front and neck flap back. I found out years ago while running in the Kring Point area (swampy area with LOTS of deer flies) that if I put a running singlet under my hat and let it drape down behind me that deer flies will not bite. Works every time.

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