They bite, they pester, but here’s why I love them anyway
While hiking through the forests of central Vermont last summer, I came under aerial assault by a battalion of flies with kaleidoscope eyes. Deer flies had come in for the attack. This is a normal situation to find yourself in when you reach an opening along a forested trail. They whirl around your head like moths around a porch light. For a while they seem like they are uninterested in landing; instead, they’re laser focused on approaching close enough for you to hear their irritating buzz, yet just far enough away to avoid being swatted. And after you begin to accept them as a harmless nuisance, they sneak their way onto your skin, delivering a painful bite. You won’t even notice until they’ve already taken off, leaving a little drop of blood oozing from the open wound they’ve created.
Despite all of this, I do not hate deer flies. I sometimes wish they would leave me alone, but I am fascinated by their acrobatic agility, their incredible life history, and especially by their hypnotic eyes. The compound eyes of the deer fly are actually made up of hundreds of small cells called ommatidia which each function as separate visual receptors. Together, they form the ‘compound eye,’ which combines the images from each ommatidium to form the image that the fly sees. In most deer flies, the ommatidia are different patterns of iridescent color. The reds, blues, greens, and blacks swirl together to form intricate and beautiful patterns.
Once you get past their eyes, you can go on to appreciate some of their other qualities, such as their phenomenal aerial agility. Like all other flies, deer flies have just one set of wings. Some ancient ancestor of the flies once had two pairs, but the rear set evolved into small, club-shaped appendages called halteres. These halteres act as gyroscopes, giving them great balance and control when in flight.
After a deer fly has spotted you with its beautiful eyes, used its incredible flying ability to land on your head, and successfully stolen a drop of your blood, what it does next is even more amazing. Only female deer flies actually drink blood. They use this blood meal to obtain the nutrients required for laying eggs. It is with that little extra help from you that the deer fly is able to complete its life cycle.
This is why when a deer fly lands on my head, I swipe rather than swat. While I’d rather not be the blood donor for a needy deer fly family, I don’t want to squish them either. They are amazing creatures that deserve our respect and admiration. And even if I tried to squish one, I probably couldn’t catch it anyway.