Spiders are interesting creatures.  They don’t rely solely on their muscles to move.  They rather use a combination of hydraulics and muscle coordination to get around.  Muscles flex their many legs and hydraulic pressure extends them.  This adaptation allows spiders to be excellent leapers. Some can jump more than 50 times their body length because of the way they extend their legs.  That’s power!

This innovative approach to movement can cause problems.  First of all, as theirs are hydraulic systems, anything that causes a drop in blood pressure will severely limit their ability to move.  Another problem is the impact temperature can have.  Like all liquids, a spider’s blood (hemolymph) is affected by changes in temperature.  As its viscosity changes with temperature changes, the spider’s ability to move is impacted.

A recent study of tarantulas showed that at lower temperatures, when the hemolymph is thicker, the spiders move slower.  When it is hot, they move faster but are much less coordinated.  It would be hard to notice this without help.  Spiders can move very quickly, but scientists are able to measure their dexterity by painting white dots on the spiders’ joints and recording their movements.  They can then look at the angles of the joints as they ran to determine how coordinated (or not) they were.  Because they are so much more coordinated at lower temperatures, some speculate this is what they stay hidden until dusk.

Researchers said studies like this help other areas where hydraulics are used, such as in robots.  Anna Ahn, one of the chief authors of the tarantula study said, “Hydraulic extension has its limitations. And the limitations happen at the faster speeds, rather than the higher fluid viscosity.”