Lisa Marceau, age 11, of Waterville, N.Y., for her question:

WHY DON'T NIGHT CRAWLERS COME OUT DURING THE DAY?

The earthworm's skin is thin and very delicate. It must be kept moist and fairly cool, otherwise it dries up and and this is fatal to the worm. Things are just right for him down there in his dark burrow, where the air is cool and damp. But a short spell upstairs in drying air steals all the skin's moisture  and just a few minutes of bright sunlight may be fatal. For this reason, the night crawler and his wormy cousins stay below during the sunny hours.
True, the worm's skin seems to be too fragile to be any use at all. This is far from true. That delicate skin can sense certain chemicals  and the worm knows which ones to avoid. It also has numerous cells that detect light and darkness. They inform the worm on topics such as which way to turn to avoid a sunbeam. The skin that must be kept moist in order to survive knows just what to do to take care of itself. And a wise worm leaves his burrow only after sunset or before sunrise.