Home > Articles

  • Print
  • + Share This
This chapter is from the book

Let sleeping spiders lie

"To sleep, perchance to dream," pondered Shakespeare's Hamlet in his famous "To be or not to be" soliloquy. He was contemplating what happens after people die, but sleep researchers get equally ponderous about why we need sleep and whether sleep and dreaming are universal across the animal kingdom.

Even single-celled organisms have a circadian rhythm, a daily pattern of activity and inactivity. Spiders do, too. Some spiders are active during the day and inactive at night, and others are active at night and quiescent during the day. Of course, an inactive spider is not necessarily asleep.

Sleep is defined as a period of inactivity with reduced responsiveness to sensory information that is rapidly reversible (unlike hibernation or a coma). To be considered sleep, the rest period must also be homeostatically regulated—that is, disrupting it creates an increased need for sleep.

No published studies have measured changes in spiders' behavior when their rest period is disrupted to determine whether it meets the strict definition of sleep. Anecdotes from tarantula owners that their pets are sometimes difficult to rouse suggest that they sleep.

Laboratory studies on fruit flies also support the notion that spiders sleep (or, at least, that invertebrates sleep). Fruit flies have periods of inactivity in which they are unresponsive to small vibrations that would ordinarily make them respond. During the inactive state, gentle tapping on their container disturbs them. If they're deprived of a night's rest this way, they compensate by resting more the next day.

Not only does their behavior fit the definition of sleep, but it also bears similarities to sleep in mammals. Young fruit flies need more sleep than older fruit flies, and sleep is more fragmented in older flies. Mutant insomniac flies exist. In addition, caffeine, antihistamines, and amphetamines have similar effects on sleep and waking in flies as they do in mammals. As appears to be the case in mammals, the activity of about 1 percent of genes in flies is different during sleep than during wakefulness.

Researchers are not particularly interested in drowsy fruit flies. They are using fruit flies as a tool to understand the genetic and biochemical mechanisms that control sleep, with the goal of developing ways to treat sleep disorders in people.

No one knows whether fruit flies and spiders dream of each other, or anything else. The scientific literature does not contain any reports of invertebrate rapid eye movement (REM) sleep—the type associated with dreaming.

  • + Share This
  • 🔖 Save To Your Account