As unnerving as it may be for some, the scuttling movement of tarantulas is a rather impressive feat. All eight of the animal’s hairy appendages are controlled not by muscles, but by a hydraulic fluid called hemolymph, which flows through the legs and causes them to flex and extend. While this system is simpler and lighter than muscled movement, it is also more sensitive to temperature changes. This could have direct implications for the speed of the skittering critters and for robots designed to mimic their movement, researchers write in The Journal of Experimental Biology. In the new study, they tested Texas brown tarantulas' (Aphonopelma hentzi) speeds across a variety of temperatures. The hotter the temperature, the faster the spiders sprinted. Speeds at the highest end of the tested range—40°C—were 2.5 times faster than speeds at the lowest end of the range—15°C. The researchers found that the difference was caused simply by faster stride frequency. The researchers had hypothesized that when temperatures were either too cool or too hot, the spider’s joints would lose their ability to work together synchronously, but, surprisingly, the leg joints were most tightly coupled at low temperatures and slow movement speeds. As things heated up, the actuation of the joints was less precisely coordinated, but the spiders still moved faster. The team proposes that this decoupling may reflect an incomplete flow of hemolymph in and out of the limbs, suggesting that the spiders' top speed is set by the limits of how quickly the fluid flows.

A link to the study will be added once it is available from the journal.

(Credit for first linked video: F. Y. Su and N. A. Booster)