Kevin Carr, age 12, of Belmont, N.C.,, for his question:

Why doesn't a spider get caught in her own web?

A spider can scoot across her web with the greatest of ease. But a fly becomes entangled in a sticky net of threads as soon as he touches it. The secret of this unfair trick lies in the fact that some of the threads in the web are covered with a thin, sticky fluid and some are not. The cross threads, those running from the center out to the edges, are free of goo. The finer threads, which spiral around and around, are sticky booby traps.

The busy fly usually hits straight into the spiral threads of the web and gets stuck. The spider, waiting in her corner, comes tripping forth on her eight feet. Since she made the web, she knows which of the threads to avoid. She is very careful to put her feet down only on the safe, non sticky threads.