Karen Berube, age 10, of Greene, Rhode Island; for her question:

Why do flies rub their legs together?

The fly is a flighty character who usually swoops away before we have a chance to watch her. But once in a while, if you don't make a move, you may see her perch a while and wiggle her skinny legs. From the looks of things, she could be rubbing her hands together or doing her setting up exercises. Actually, the tiny creature is cleaning herself. We need a magnifying glass to see her bitsy legs and feet properly. But naturally to the fly, they are the proper size. And from her point of view they gather a lot of dust and dirt.

There are miniature bristles on her six jointed legs and sticky, hairy pads on her feet. They tend to pick up a lot of grubby dirt and several times each day the fly pauses to clean herself. The claws on her feet are used as combs and scrapers. She grooms her entire body and her legs take turns at cleaning each other. She rubs them together, somewhat as you use your two hands to wash each other.