Why flies have nipples on their eyes

Sometimes, we need a reminder to be thankful that we don't have nipples protruding from our eyeballs. Many flies, including mosquitos and horseflies, have something called corneal nipples. These are tiny little protrusions that cover the surface of their eyes. These nipples aren't the kind that produce milk, but instead, they increase the intensity of transmission and reduce glare.  Diptera expert Dr Erica McAlister explains that these eye-nipples also control how much light enters the bug's eyes, and can also have an anti-fogging effect. If only eyeglasses came with anti-fogging nipples built in.