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Category: Friendly Praise Archive

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Hydraulic Legs

Hydraulic Legs

1/160 @ f 22.0; ISO 400

Ogletree Gap Park
Copperas Cove, Texas

31 August 2009

Jim Baines

- Jim Baines

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The seven segments of a spider's legs (coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus with attached claws) make them much more flexible than human legs. Like humans, spiders have muscles that bend the legs closer to the body. However, spiders do not have muscles that move the legs away from the body. Each time a spider needs to stretch a leg back out, it must pump its hemolymph (blood) into that leg. Then, to bend the leg back, pressure is relaxed and the hemolymph flows out of the leg as the muscles do their work. This is similar to the way a garden hose gets stiff and moves around when filled with water, and then gets limp again when the water drains out. That's right, a hydraulic system for limb extension! If a spider weakens because of sickness or dehydration and can no longer maintain adequate internal hemolymph pressure it will no longer be able to extend its legs. As it weakens the loss of hemolymph will cause it to curl its legs under in a very characteristic pose reminiscent of a loosely clenched fist, commonly termed the "death curl". (The Tarantula Keeper's Guide, Stanley A. & Marguerite J. Schultz)

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September 01, 2009

countryimpressions.net - Tammy M. Anderson

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Good morning, Jim. Excellent colours and details. This is superb. No bear today either but I probably can find you one from past images. LOL.