Do bugs sleep? That's the question we discuss on today's Moment of Science. Time once again for the mail bag. Today's letter:

Dear Moment of Science: Do bugs sleep?

Signed, A Sleepless Bug- watcher.

An excellent question! I've never seen a sleeping ant, or beetle, or anything. But then, I never watched them for very long. After doing some research, I found that they do indeed go into a relaxed state at some point. But sleep is different from just resting. Neuroscientists distinguish sleep from rest by pointing to specific kinds of brain activity that take place when the body is in an immobile state.

By this definition, insects do not sleep. Neither do fish, amphibians, or mollusks. But lizards do indeed sleep, as do all mammals--that includes us humans. REM, or Rapid Eye Movement sleep, is thought to be associated with a particular kind of dreaming. We see REM or pretty REM-like sleep in all sorts of animals, not just humans.

Almost all mammals, in fact, have REM sleep; birds do too, although only in the early parts of their lives. It seems that sleep and REM are required by a particularly complex kind of brain. All creatures from Koala bears to Congressmen need actual sleep . . . whereas your average mollusk can get by with just rest.