Tarantulas Grow Clumsy When Things Heat Up

A warming world may have more of an impact on spiders than experts ever expected. That's at least according to a recent study that closely investigated how temperature fluctuations affected the movements of spiders and robots alike.

It may not seem like robots and spiders have a lot in common - that is, unless a robot were to be fashioned in the form of one. However, regardless of the shape, size, or inspiration for them, most robotics rely on hydraulic pumps for movement. Those pumps are not all that different from how spiders move their own limbs, where, in the place of muscles, they have joints that inflate with haemolymph to straighten.

Scientists have long known that fluid viscosity can increase dramatically as temperature falls, which can in-turn affect the effectiveness of hydraulics. This caused researcher Anna Ahn from Harvey Mudd College to wonder, "would the same prove true for spiders?"

"I've always wanted to study spiders because they use hydraulics," Ahn admitted in a recent release. "This is a fascinating question."

To answer it, Ahn, with the help of three other colleagues from California colleges, decided to test the running abilities of Texas brown tarantulas (Aphonopelma hentzi) in various temperatures. The researchers wanted to make sure that their data was relevant to natural circumstances, so they limited the temperatures the spiders ran in to those they would naturally see - anywhere between 15 and 40 degree Celsius (59 - 104 °F). Then, by marking the spiders' legs and recording their progression down a runway at set speeds, the researchers were able to assess the spiders' performance under these conditions.

After a stunning three months of this analysis, the researchers became certain that the spiders were indeed affected by heat, actually heavily speeding up from a slow 20 cm s^-1 to a surprising 53 cm s^-1 when exposed to the harshest temperatures. However, while getting faster may sound like a good thing, the researchers found that this also made them clumsier, with the strides of all eight of their legs no longer perfectly synched for maximum efficiency. Ahn suspects this is because there just isn't enough time for the haemolymph mechanism to fill and drain at the arachnid's top speed.

"Hydraulic extension may allow spiders to save space and mass in their limb, but it may come at the expense of control," Ahn said.

She went on to say how this might explain why tarantulas prefer to hunt just before evening, when a day's hottest temperature's have already passed.

The results of this study were published in The Journal of Experimental Biology.

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