Deer Flies - Almost The World's Most Awful Animal

:date: 2025-08-08 19:50

In the extremely prescient song Teenage Immigrant Welfare Mothers on Drugs, the Austin Lounge Lizards ask,

They then sardonically posit the answer is the titular antagonist of the song. (Seriously, go have a listen to this 1996 song which does a freakishly good job of predicting our current zeitgeist. Or you can read the lyrics.)

I'm often reminded of that song these days because the answer to that second question is, for me in our swamp, something almost as bad as fascists: deer flies. I've mentioned the insane mosquito situation (which has been better this year) and the sinister black flies. This year they have been bad at times, but now we have managed to keep those bugs out of the house, I think it's been the deer flies that have been the most maddening.

Here is one I tamed today  —  her name is "lefty".

While usually not as gory as the rivulets of blood caused by black fly bites, deer fly bites are nasty and leave cuts and inflammation. But what really can drive someone insane is their hunting behavior: they go for the back of the head. This is why if I wear a backwards baseball hat, they are pretty much neutralized. Who would have thought that fashion trend could actually be very practical?

If, however, I forget to wear my backwards hat, I'm usually about halfway through watching the dog take a dump when I hear them and feel them pecking on the top of my skull. Ironically I've thought that the most impractical hat of all time, the yarmulke, would actually not be nearly so absurd in our context. That's how weird this insect phenomenon is.

All this is to impress on you how very maddening these flies have been to me. Clearly they've pushed my limits of mental composure. I call these little fuckers, well, little fuckers for one. And also "Pig-Pen flies". This is because I have had extraordinary experiences where I've been rollerskiing or biking and a cloud of them form around my head. I can look down and see this cloud in my shadow like the Pig-Pen character of Peanuts. It's crazy.

But what's really crazy, is I can not see them directly! I also call them "gaslight flies" because they swarm you but you only hear them and feel their attacks. If you turn your head to look at them, they will move with your head as fast as you can turn it to remain out of sight. It's incredible. Sometimes I'll go to a reflective surface like a window or my bike mirror just to see them. Or you can back up to a building and then look straight up.

It's difficult to say what exact species this is but I suspect it's Chrysops excitans or something very similar. Probably it is many similar species throughout the summer.

Flies from this family, Tabanidae (horse flies), are apparently some of the fastest insects known with speeds up to 145kph. What I know first hand is that they are quite fast. Above 20kph, you can start to lose them. But below that the Pig-Pen swarm can follow you for many kilometers. Below about 15kph, they can land and be very annoying.

I have done experiments with a hard hat where I put a sticky fly sheet on the back. With only that I've caught quite a few. The internet seems to believe that they are attracted to blue (though more scholarly work seems to be more likely to mention "polarized light"). I did a little experiment making a pair of blue animal ear shapes on my hard hat and putting the sticky sheet over that. Just biking to the mail box (maybe 4 minutes of very moderate biking) I got two that I never saw or heard.

Ultimately you can defend against these simply with a hat and if they really drive you crazy, you can go on the offensive. But they are so incredibly maddening that they give the other deeply nasty bugs of our forest some real competition in the world's most awful animal contest.