Listen to part of a lecture from a biology class.

Listen to part of a lecture from a biology class.
Professor: In the environments they move around in, insects are regularly exposed to various particles like dirt and other substances which can cling to their bodies and cause problems, like making it harder for them to move around or fly, and of course, if insects can't move around or fly easily, it's hard for them to accomplish the activities they need for survival. So insects have developed certain ways, certain mechanisms to keep their bodies clean, which can be categorized as being either active or passive. So first, active ways, these are cleaning mechanisms that insects actively use on a regular basis in an effort to clean themselves, removing dirt and other particles from the surfaces of their bodies. And they may have special body parts adapted for this purpose. For instance, when bees visit flowers to gather pollen, they can get pollen in their eyes, which makes it difficult to see while flying. Their front legs, though, are covered in bristles like a brush, and they use their front legs to clean the pollen off, brush the pollen out of their eyes. But insects also have passive cleaning mechanisms. Insects don't have to make any effort to use these. So like certain insects, have body surface that are shaped in a way to allow particles and dirt to be removed continually, passively, without the insects having to make any effort to remove them. For example, cicadas. If cicadas’ wings get covered with dirt, it's hard for them to fly. Luckily, their wings have a special bumpy surface that repels water, so when rain water or dew drops on their wings, the water rolls off and carries the dirt along with it.