John Wilder, age 15, of Houston, Texas, for his question:

Why does a fly rub its legs together?

It is a good idea t o study these small creatures with a magnifying glass or, better still, with a hand lens. This way we can see how their tiny bodies are made and what is needed to keep them in trim. The fly’s feet, all six of them, are small miracles of nature.

Instead of toes, each little foot ends in a pair of miniature pincers. The legs are covered with bristles and there are sticky pads under the feet. The little creature wears a shoulder cape of fuzz and there is more fuzz under his body and on his face. All this hairy fuzz attracts dust and dirt and, if it were not removed, the little aerial acrobat would soon be too heavy to fly. When he rubs his legs together, he is using his pincers to clean himself.