In particular, I can believe that flies are spooked by specific patterns of light and dark. They seem so hard-wired in their behavior, they probably can't help themselves.
When I was little, we had an egg ranch, which meant we had thousands of chickens, and lots and lots and lots of flies. I remember one day sitting in the garage, minding my own business, when a fly started to buzz around the main opening. It flew toward a side window, then veered toward me, heading right for my ear. I jabbed at it, which made it fly away from me and back to the main opening. It turned around, and repeated the same looping pattern toward the window, then my ear, then back out in reaction to my jab. It (and I) did the exact same thing at least 6 times in a row. The first couple of times I just reacted; the last few times I purposely stayed in the same spot and repeated the same jab because I couldn't believe the fly could not learn its lesson. I finally broke the pattern somehow (I think I just covered my ear), and the fly stopped bothering me.
Several places online assert that flies are incapable of learning, for example this site which says "Despite years of trying, no researcher has ever been able to teach flies anything - fish learn, ants learn, snails learn, cockroaches learn, even worms learn ... but never flies." I couldn't find any support for this assertion- but I totally believe it!