DECEMBER
2004

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

12-22-04

Do Insects Sleep or Are They Just Feigning It?

Humans do it. Or at least try. So do other animals. Even some plants do a similar thing. All living things in the world, it seems, need sleep. So what is sleep?

Researchers who worry about the inability of some humans to sleep define it this way: It is a reversible behavioral state of perceptual disengagement from and unresponsiveness to the environment. OK, if you can't sleep, and counting sheep doesn't ease you off into never-never land, just try repeating the definition 20 or so times!

People have long recognized that sleep is important to animals. We even have sayings that reflect our observations. "Let sleeping dogs lie," for example. The idea is that if you wake a sleeping dog the startle response that results might end up in a dog bite. This is not a new saying. It was first written by Chaucer in 1374, "It is nought good a slepyng hound to wake."

It is easy to observe dogs and cats sleeping. We even imagine that dogs, like humans, have dreams. And anyone who has ever been around a soundly sleeping dog can attest to the fact that canines snore. We even equate some of our sleep habits to those of animals, for instance, the idea of a catnap. 

There are many sayings that relate to human sleep behavior. For instance, the description that someone is "sleeping like a baby." This saying has prompted many a wag to retort that anyone who would say that probably hasn't been around babies for a while! College professors have been defined as "someone who talks in someone else's sleep!" Shouldn't that be a preacher?

Sleep is accompanied by a slowing down of physiological processes. Heart rate and breathing patterns slow down. Researchers have been able to verify sleep in animals by recording brain waves. It is not so easy to determine if insects sleep. Historically, entomologists have reported seeing insects that appeared to be sleeping. At least, they appear to be in a comatose state.

We know insects become less active at low temperatures, even at times going into to a state of suspended animation known as hibernation. A lot of insects, including the familiar lady beetles, hibernate. But are hibernating insects asleep for a winter nap? Day-active insects become inactive at night. Some paper wasps appear to sleep at night, away from their nests. When they do this, they seem to be lethargic compared to the way they behave during the light hours.

Some types of butterflies appear to sleep at nighttime. During their southern migrations, monarch butterflies congregate in groups at nightfall, fold their wings and appear to catch a few winks before the next day's journey. Dragonflies also seem to rest at night. At least, they appear less alert and are easier to catch at this time.

Some scientists believe that the widespread animal behavior called death feigning is a form of sleep. Death feigning is known, in popular language, as "playing 'possum" because 'possums are so good at it. Many other animals feign death, including crustaceans, reptiles, birds and insects.

Many caterpillars assume strange postures when disturbed. For instance, a cutworm curls in a ball and plays dead. The well-known crustacean called a sowbug is also known as a pillbug because it curls up and feigns death when bothered. Beetles are also good at feigning death. They draw their legs close to their body, drop from the plant and fall on their backs, looking like a dead insect.

So how long will an insect play dead? Most feints are of short duration, a matter of minutes. But in some insects the feint lasts for hours. The world record feint for an insect is 8 hours by a giant water bug. That is a feint that sounds like a good night's sleep to me!

 

Writer: Tom Turpin
Editor: Olivia Maddox