This fiercely important question was actually asked by our own David Tracy, who’s driving his minivan somewhere in Germany (I think), likely succumbing to a particular strain of road madness. Otherwise, why else would he be reaching out to me, clearly distraught, wondering if the fly that he just let out his window survived? Either he confided things to that fly and considered it a trusted friend, or he confided things to that fly and now hopes it’s dead, taking his secrets to the grave. Either way, it’s a good question, so let’s find out.
I think we’ve all been in this situation: you’re driving along at normal highway speeds of at least a mile-a-minute or more, when you notice a fly flitting around in your car. Since you’re not some freaking insect Uber, you decide to tell that fly to take a hike, and you roll down your window. At some point, the fly will notice the open window, and exit your car, where the fly, moving at a speed of, say, 70 mph, will impact a vast mass of air.
So what happens then? I suppose it’s the equivalent of a stationary fly suddenly being blasted with 70 mph winds. We’ve seen how tiny insects like flies fall relatively slowly and usually harmlessly to the ground from significant heights because the density of air and their small size slows them down—in a vacuum, as you probably know from the astronaut, that feather, and that hammer, everything falls the same speed.
The significant impact of air density on little insects would also likely mean that the mass of air hitting the fly would have a pretty significant, even violent effect on the fly, wouldn’t it? So, what happens to these flies? Do wings get torn off? Are antennae sundered, legs wrenched away, leaving just a helpless head and thorax and abdomen to bounce onto the pavement?
I think even if there’s a certain amount of air being pulled along with the car as it speeds down the road, at some point in this interaction we have a fly moving at speeds far, far beyond its original design specifications and encountering a very high rate of airflow.
I don’t know for certain what really happens to the fly, so I decided to reach out to an expert. I called an etymologist.
The etymologist told me I was an idiot, angry at both being woken up and not even for the right reasons, as I needed to call an entomologist, who studies insects, and not an etymologist who studies words, words like “simpleton” and “don’t ever call me again.”
So, I reached out to Dr. Wes Watson, a Professor of Entomology at NC State University, and asked him how flies fare when being slammed into air masses at highway speeds.
“They’ll survive,” Dr.Watson told me, with a lot of confidence, and, I detected, more than a little respect for common flies.
Dr.Watson told me that he’s seen flies that survive 100 mph hurricanes and tornadoes and, as long as they don’t impact anything hard, they can take severely violent wind barrages without experiencing any real harm.
Wings remain anchored, as do all of their other tiny appendages, as fly anatomy is surprisingly robust. He even told me about the clue to seeing how old a fly is: check the edges of the wings.
Because flies are so generally durable, the only place that exhibits any real wear and tear are the edges of their wings, which tend to get frayed and fragmented over time, so an old fly (that means in the wild, about two weeks, up to a month in captivity) will have wing edges that show a bit of wear.
He also mentioned that a fly’s feet have structures, known as tenent setae, that allow for incredible grip on surfaces, even seemingly smooth surfaces like windshield glass.
See that picture up there? That’s an electron microscope image of a fly foot, and those fuzzy pads are covered with the tenant setae, which have a massive amount of surface area to grip almost any surface. The big claw things there aren’t so much to grab and hold onto a surface, but more to pry off those footpads!
We’re getting a bit away from the original question because flys are much more impressive than we generally give them credit for, but the takeaway here is do not worry about the fate of flies that you’ve launched from your car at 85 mph. They’ll be just fine.
I hope this frees many of your from the burden of guilt about possible fly-murders. I know my conscience feels more clear, and I hope David’s will, too.