Horse Flies and Deer Flies

By , June 7, 2010

We knew they’d come eventually. The predominantly sunny, warm weather had to bring horse flies and deer flies sooner or later, and now they’re here in force.

There are slight differences between horse and deer flies, not easily recognized, and in the end, inconsequential. What matters is that both of them are big flies, up to around an inch long, they swarm during hot, dry weather, and both bite horribly. As a regional naturalist puts it, the only good thing about them is that they take so long to bite that you can usually swat them before they get around to it. When they do, they stab with a big, sharp tongue. I’ve lived more than 30 years in Alaska, and I don’t believe I’ve ever had a complete fly bite, but I’ve had plenty of bites started, and that’s painful enough!

Because they seem to need fair weather, they don’t come around that often. Unfortunately, they thrive when the weather’s right for swimming or other activities that expose a lot of skin. They swarm close to water, and are mysteriously attracted to the color blue. One or two of them can quickly ruin a good day of fishing. If they find you becalmed in a sailboat, they’ll torture you.

We actually saw a few flies before Sunday, when they got thick. I don’t know what kept them, but I suspect it’s a type of hornet we commonly call yellow jackets. One of the first summers we owned the homestead, Haines experienced a yellow jacket “epidemic.” On one visit, we were plagued by flies, but on the next, they’d almost completely disappeared. One morning as I explored the rocky beach, I saw yellow jackets patrolling the areas horse and deer flies usually frequent. I think they were hunting the flies!

Dragonflies are avid fly eaters as well, and the flies know it! When we installed one of the picture windows, we managed to time it between fly hatchings. We knew when they next hatched, because the weather was sunny the whole time. On one particular afternoon, the flies suddenly began to swarm. At that moment, I was holding a 4X6 picture window in place by myself. I watched helplessly as the flies circled. Suddenly, the shadow of a large dragonfly streaked across the wall in front of me, and the flies immediately disappeared. Newly hatched, they recognized the silhouette of a killer! We really liked dragonflies before this happened. Imagine how our esteem for them increased that day!

Like all the other biting insects, and things that dampen our enthusiasm now and then, horse and deer flies are annoying, but not that significant in the long run. The memory of even the worst swarms soon fades when sunny summer days are recalled.

4 Responses to “Horse Flies and Deer Flies”

  1. Wade says:

    I just happened upon your website and haven’t had time yet to look around much; – just read your bit on deer flies and horse flies. Keywords that brought me to your site are “difference between deer horse fly.” You may be interested to know that you are the second or third or fourth hit.

    I’m curious, where did you hear or how did you otherwise learn that these flies are attracted to the color blue?

    Anyway, I enjoyed your little article.

  2. Mark Zeiger says:

    Hi Wade, the attraction to blue is local folk wisdom. A friend from Sitka, who has some truly horrid horse/deer fly stories to tell, was the first to mention the wet blue towel strategy to me several years ago. We’ve experimented with it enough to believe it’s true, but of course, we’re not scientists.

    I mentioned recently that we had a hatching of flies while burning slash on the beach. I sweated until my shirt soaked through, while Michelle stayed dry. I got swarmed by the flies, but they left her alone, which backs up their attraction to wet as well. Also, the shirt I wore was purple, so apparently they’re not too picky about shades . . . ?

    I’m pleased to know that that articles so high on the search lists. I try not to obsess over keywords, or other methods of pulling in readers, but I’m always pleased when they visit the blog. Thanks for checking it out!


  3. Wade says:


    Thanks for getting back to me. I’m not sure, but there may be something to the “myth” (of deer/horse flies being drawn to the color blue). I was talking yesterday to a customer (I work at a canoe livery – Northland Outfitters – in Upper Michigan)about these flies, and he said that he had seen, downstream at a backwoods campground, a flat triangular-shaped object, maybe 18-24 inches on every side, posted on a tree. He said this object, this sign of sorts, was sticky and a bunch of flies were stuck to it. Most importantly, he said the sign was purple in color. I said, “Well golly gee george, are you sure it was purple and not blue?” He wasn’t so sure.


  4. Mark Zeiger says:

    Hi Wade, I need to make a very important distinction between “folk wisdom” and “folklore.” The latter has become equated with falsehood in modern society, (although I think we often make a mistake in dismissing it as such). By folk wisdom I meant that non-scientists have discovered through experience that this works, but as far as I know, it hasn’t been sanctioned, if you will, by scientific research. One day, they’ll announce on the news that, after a multi-million dollar study, science has confirmed that these flies act this way. Alaskans will join outdoors people from around the world in answering with a resounding, “Duh!”

    I’m intrigued about the purple item, though. Blue and purple are close enough that I assume the flies, if attracted to one, will flock to the other as well (as in the purple shirt I wore while burning slash). My favorite color is blue, Michelle and Aly’ like purple, so we have plenty of both on the homestead. In the words of the great Ben Franklin, “let the experiment be made!” I’ll suggest this to Aly when she gets back from Canada. Maybe we’ll have a follow-up blog post on it!

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