Deerflies

Illustration by Adelaide Tyrol

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.

Download the Article
 
Discussion
  1. Brian Kenefick → in Nova Scotia
    Aug 28, 2017

    Here in Lunenburg County, Nova Scotia, we too suffer from deer fly attacks. However, our solution is locally made dragonflies, the natural predator of our deer fly.

    They are made from bobby pins for the body, white foam for the wings, blue foam for the head, and the body is wrapped in green string which also ties the finished dragonfly to the safety pin then you attach the fly to your hat. A pair of these work wonders; all you have to do is turn your head a little so the deer fly can see the dragonfly, and they veer off like a jet aircraft avoiding ground to air missiles. No killing required.

  2. Thorne Bill
    Aug 28, 2017

    Terrific practical article. Thank you.

  3. Declan McCabe → in South Burlington VT
    Aug 29, 2017

    Brian,

    That’s genius.  I’ll certainly give it a try.  Looks like someone makes a commercial version http://getyourbug.com/

    But your instructions are more than enough for me to crank out a few for the lab.

    Thanks

    Declan

  4. Daniel Wing → in Corinth, VT
    Sep 01, 2017

    The article did not mention specifically that deer and horse flies are ambush predators that respond to visual cues.Unlike mosquitoes, they do not follow scent plumes. The population of deer flies at any one location is relatively low, although it does not seem that way when they are attacking. Go to Youtube videos to learn of research on effective control strategies.

  5. John McNerney → in Monkton, VT
    Sep 01, 2017

    Deer flies are strongly attracted to some shades of blue (New Holland Tractor blue, or the blue on a plastic disposable Solo drinking cup are a couple of good examples). For this reason, all of my blue shirts get put away during deer fly season.

    They are also attracted to motion, 10 feet or less from ground level. They will go for the high point on their target first - which is why they are constantly buzzing around your head, getting in your hair and biting your head and neck. (So put away that blue baseball cap during deer fly season)

    A University of Florida professor has made a study of their behavior, which resulted in some deer fly trap recommendations. One of these involved attaching a blue Solo cup your your hat and coating it in sticky goo (Tanglefoot is one recommendation). The flies are so attracted to the blue cup that they leave you alone. See the article here:
    http://entomology.ifas.ufl.edu/pestalert/deerfly.htm

  6. Jeremy Schrauf → in West Wardsboro, VT
    Sep 01, 2017

    I must be missing something.  I read “Because greenheads emerge only from saltmarshes, we know they travel up to two miles in search of blood.”  As far as I know no part of the Winooski River is within two miles of any salt marsh.

Join the discussion

To ensure a respectful dialogue, please refrain from posting content that is unlawful, harassing, discriminatory, libelous, obscene, or inflammatory. Northern Woodlands assumes no responsibility or liability arising from forum postings and reserves the right to edit all postings. Thanks for joining the discussion.

Please help us reduce spam by spelling out the answer to this math question
two plus two adds up to (4 characters required)