It may seem unbelievable, but when a cockroach is strolling across the wall of your house — like right next to the ceiling, you know how they like to do that — the roach is not, in fact, trying to find the most advantageous angle from which to launch itself off the wall and onto your face. Although it sure does seem that way at times, right?
Cockroaches have been around for about 320 million years, so there was an unbelievably long stretch of their evolution in which flying at a human's face wasn't even an option. More than 5,000 cockroach species exist on the planet today. Their behavior can vary widely from species to species, but most cockroaches are nocturnal — in fact, the name of the order of insects that includes cockroaches and termites is Blattodea, which in Latin means "insect that shuns the light." You're not even around when most cockroaches start dive-bombing stuff.
However, a lot of tropical cockroaches fly by day, and some nocturnal species are attracted to light, much like moths. For instance, North American cockroaches of the genus Parcoblatta are very attracted to light, but only the males can fly. So do they intentionally fly at our faces?
"No!" says Dr. Coby Schal, an entomologist in the Department of Entomology & Plant Pathology at North Carolina State University whose Schal Lab specializes in cockroaches. "These cockroaches fly to bright objects, and when we sit on the porch at night, with a light above us or behind us, our head and face create a lighted halo — sort of like an eclipse. Insects may be attracted to this light."
And unlike blood feeders like mosquitoes, bedbugs and fleas — or like moths that can sense the gases emitted from flowers — cockroaches probably can't sense the carbon dioxide we exhale.
"I am not aware of any experiments that show that roaches are attracted to CO2 or to humans or human-produced odors," says Schal.
So rest easy: Cockroaches want nothing to do with you. Your leftovers or your beer, though? That's another story.