I've noted that flies in my house have no problem landing on even perfectly clean mirrors. Why don't they fly straight into them? Can they sense that there is a surface there, even though they can't see it?
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$\begingroup$ I think it should be glass rather than mirrors $\endgroup$– user1357Commented Jul 26, 2014 at 20:48
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$\begingroup$ @casey Yes, but flies will often fly into a window, while the same fly will land on a mirror. $\endgroup$– J. MusserCommented Jul 26, 2014 at 21:11
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$\begingroup$ Maybe fly vision isn't very good, but good enough to see the outside through the window, while a mirror reflects the wall across from it, so it looks like a wall. Try to put a mirror across from a window and see if flies treat it like a window. $\endgroup$– user137Commented Jul 27, 2014 at 6:02
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$\begingroup$ @user137 Hmm, interesting theory, but if the fly has any depth perception, wouldn't it see the wall (if it can) as far away? It has no reason that I can see to know there is a surface at that point $\endgroup$– J. MusserCommented Jul 27, 2014 at 6:29
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$\begingroup$ @J.Musser, That's why it's an experiment, I don't know anything about the visual acuity of flies. Maybe the mirror reflects more glare from the lights around it, while a window appears to have less reflection because any reflection would have to compete with sunlight behind it. $\endgroup$– user137Commented Jul 27, 2014 at 6:37
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It might be pretty straightforward. Common window/mirror glass is opaque to UV, so as far as the fly is concerned mirrors are just translucent surfaces.
This of course leads to the question of why flies can't see window glass. Maybe the large amount of light passing through at visible frequencies makes it look like a tinted fog to the housefly? Maybe they're trying to fly through mirrors too, but land on their feet and just roll with it?
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2$\begingroup$ First link doesn't appear useful anymore. $\endgroup$ Commented Sep 1, 2015 at 20:32