Ever wonder why bugs are so bug-eyed? Maybe it's because bugs don't ever get any shut eye.
While a still bug might look like it's dozing, the creepy crawler is merely relaxing. Neuroscientists distinguish sleep from rest by pointing to specific kinds of brain activity, like dreaming, that take place when the body is in an immobile state.
According to neurological criteria, insects do not actually sleep. Neither do fish, amphibians or mollusks. Lizards and mammals, on the other hand, need to catch their z's.
REM, or Rapid Eye Movement, sleep is thought to be associated with dreaming, and is required by a particularly complex kind of brain. REM sleep is common to humans and nearly all mammals. Birds also get REM sleep, but only in the early part of their lives.
Koalas and Congressmen alike need their shut-eye to recharge, while your average mollusk and insect stay OPEN 24 hours a day.
But don't let the thought of those sleepless critters keep you awake at night. Otherwise you might look a little bug-eyed yourself.