Don't Count On It

Do spiders dream of eight-legged sheep?

By day, jumping spiders hunt their prey, stalking and pouncing like cats.

When the lights go down, these pea-size predators hang out - and maybe their minds spin dreams.

As they twitch their legs and move their eyes, Evarcha arcuata, a species of jumping spiders, show something reminiscent of rapid eye movement [REM] sleep, researchers reported in the Proceedings of the National Academy of Sciences.

REM is the phase of sleep in which most human dreaming occurs.

The study suggests that REM sleep may be more common than realized across animals which may help untangle the mysteries of its purpose and evolution.

Daniela Rossler, a behavioral ecologist in Germany and one of the study's authors, was surprised when she noticed that jumping spiders sometimes dangled upside down during the night.

Dr. Rossler filmed the resting arachnids and noticed other odd behaviors. ''All of a sudden, they would make these crazy movements with the legs and start twitching,'' Dr. Rosseler said

''And it just reminded me immediately of a sleeping - not to say dreaming - cat or dog.''

Such jerky movements in limbs are a marker of REM sleep, a state in which most of the body's muscles go slack and the brain's electrical activity mimics being awake. [ Carolyn Wilke ].


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