The only good deer fly...?
Deer flies are my least favourite part of summer. I suspect I’m not alone in this respect. If you spend any time in or near forests or wetlands in Ontario in late June or early July, there’s a good chance you will have a squadron of these little attackers circling your head. They are nature’s version of the F-18 fighter jet, and once they lock onto you, they are relentless. Their preferred targets are your head, back of your neck, ears, and face, but they will happily settle on any exposed skin. Once they land, they use their razor-sharp mandibles to make an incision in your skin, salivate an anti-coagulant into the wound, and lap up your blood. Unsurprisingly, a deer fly bite itches like heck, and can leave a welt for several days.
I live alongside a woodlot with a stream running through it – prime deer fly habitat. Simply walking outside on Sunday morning to collect the morning paper can attract a few, and a walk in the woods without long sleeves and a hat tends to be a brief one. I took the hound for a stroll tonight around the perimeter of the forest and found the deer flies especially bad, prompting me to do a little research on them.It seems my big mistake tonight was wearing a blue shirt, for apparently these ladies (it is only the females that bite) are attracted to the colour blue. I also wasn’t wearing a hat, which allowed them to land in my hair and leisurely burrow down to my scalp. I managed to smash a few of them, but any deer fly-rights activists reading this will be pleased to hear they scored more direct hits on me than I did on them.
Ordinary insect repellent of the type that repels mosquitoes is in my experience less effective on deer flies, unless you’re prepared to practically bathe in DEET. Even then, the moment the back of your neck gets sweaty – as it will inevitably do on a sunny day – the deer fly’s preferred landing pad is free and clear once again. An internet search of alternative ways to prevent deer fly bites turns up quite the range of home remedies. One school of thought suggests wearing a blue hat slathered in glue or another sticky substance. Online videos show that sticky blue ball caps, hard hats and pails worn on the head can indeed become quickly covered in dead and dying deer flies, although this does create a new problem of having to have a multi-week supply of disposable blue hats/buckets (or wear the same fly-encrusted one each day). Plus there’s the fact that neighbours and family members who see you will think you are a complete lunatic. A variant on this method is to attach a sticky blue cup or rolled up duct tape sticky-side-out to a hat you want to wear more than once. It’s not quite as effective at catching flies, but is probably similarly effective at repelling people.
Effective, yes. Stylish...?
While the nuisance factor of deer flies is obvious, it’s worth asking whether they provide any valuable ecological goods and services. They provide at least two, so far as I can tell. First, they’re part of the forest food web; just how important is difficult to say. Deer fly maggots are carnivorous and eat smaller creatures found in the mud where they hatch; in turn, deer fly larvae and adults are food for larger animals like amphibians, birds and dragonflies. Second, female deer flies may eat blood, but the males feed on plant nectar, and are pollinators of various forest plants. That’s an important ecosystem service. I wasn’t able to find any studies assessing if they might also be significant pollinators of orchard crops of agricultural value (since deer flies aren’t commonly found in dry open areas, they are probably not significant pollinators of flowering garden or field crops). Given that many of our other important pollinator species are in decline – bees and butterflies in particular – the precautionary principle may be in order, meaning that we’d best not eradicate deer flies with our blue hats and vodka-based insecticides, much as we may be tempted to do so.