We have an electric fly swatter—a fly zapper, if you will—that looks like a tennis racket. There’s a button on the handle that feeds the mesh part with enough juice to execute a fly with a satisfying crackle.
I’m sure it works great, but there is a small problem. As soon as I put my hand on it, before I even pick it up, an annoying fly will disappear, suddenly having business elsewhere.
In a way this is satisfying, for if I can’t zap the fly, I can, at least, intimidate it. However, when I remove my hand from the zapper and get engaged with the book I’m reading, the fly returns, buzzing about me in its former annoying fashion.
I have tried inching my hand toward the zapper, but the fly is too smart for such subterfuge. He goes away until I remove my hand and get distracted by my book.
Over the years, I have noticed similar fly behavior when using a regular, old-fashioned swatter: Fly is being annoying, pick up the swatter, fly disappears. Set down the swatter, fly reappears.
This led me to investigate two aspects of fly behavior. One, does a fly sense my intent and react preemptively? And two—unrelated, but interesting—how does a fly land on the ceiling?
To my dismay, the internet was all but silent on the first question. I found one site with this topic: “Every time I pick up the flyswatter, the fly leaves. Why is this?” The writer said, “They will be buzzing around having no care in the world, then as soon as I pick up the flyswatter, they are nowhere to be seen.”
A few people in the comments agreed, but the discussion soon went off the rails with talk of dogs hiding at the sight of a fly swatter and cats being intimidated by spray bottles.
And that was it for question one.
There was much more information on the second question. There have been studies, including slow motion photography, that explain how a fly, though it is not able to fly upside down, can, nonetheless, land on a ceiling.
The method is easy to demonstrate with a piece of playground equipment. A child runs towards a horizontal overhead ladder, grabs a rung, and holds on. The forward momentum of their body makes it easy to swing their legs up and hook onto another rung with both feet, thus hanging, like a fly on the ceiling, facing the opposite way they were traveling.
A fly will go upward at an angle, reach over its head with two front legs, latch onto the ceiling, and then use forward momentum to swing up and grip the ceiling with its other two sets of legs. There is a variation to the technique, but it still involves grabbing hold and swinging into position.
These maneuvers are tricky, and flies don’t always stick their landings. Watching slow-motion footage of failed attempts allowed me to laugh at flies that so often laugh at me.
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