TIME

March 20, 1944 12:00 AM GMT-4

How does a spider stretch its legs? That question is an old zoologist baffler. Spiders have no leg-stretching muscles, yet they have an unquestioned ability to unflex all eight pedal extremities. A Caltech biologist, after long study, has finally solved the riddle: the answer is blood pressure.

With delicate and precise instruments, Biologist C. H. Ellis studied many kinds of spiders, including tarantulas and the poisonous black widow. Microscopic examination of their leg membranes, joints, tissues and nerves got him nowhere. But he noticed that even a dead spider leg would stretch if he squeezed it gently. He then injected liquids into spiders’ legs with a superfine hypodermic and got some very satisfactory stretching. When he dehydrated spiders by keeping them for several weeks without water, they lost their stretching ability and walked with bent legs.

Eventually Ellis discovered, from the way blood spurted from a tiny puncture, that spiders have high blood pressure. Somehow they seemed to be able to raise or lower the pressure in their legs. When Ellis bled a spider, its leg stretching became much weaker. In a report of his findings in the Biological Bulletin, he noted another curious fact: “Spiders nearly always die with their legs completely and permanently flexed.”

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