Meeting Abstract

91.1  Friday, Jan. 7  Roll with it: how tarantulas turn over MCBRIDE, JA; CHADWELL, BA; ASHLEY-ROSS, MA*; Wake Forest University rossma@wfu.edu

Like all arthropods, tarantulas (large spiders of the family Theraphosidae) must shed their exoskeletons in order to grow. When ready to molt, tarantulas roll onto their backs and laboriously “shrug” out of the old exoskeleton. Following the molt, the spider must right itself – turn over from its back to standing on its eight legs. The question is “How do they do it?” – tarantulas have a low-slung posture and are thought to lack appreciable twisting ability in the legs. We used high-speed video to capture righting events in Chilean Rose Hair tarantulas (Grammostola rosea) that were placed on their backs. Marker points were painted on the cephalothorax and legs to allow tracking of body and leg movements. The spiders’ movements in three-dimensional space were reconstructed from videos captured using multiple, time-synchronized and space-calibrated cameras. The roll and pitch of the cephalothorax and joint angles of each leg were tracked throughout the righting event. Analysis of the videos showed that the tarantulas always flipped over by rolling, but the direction of the roll (to the left or the right) and use of the legs were highly variable among trials. One consistent feature was that, on the side toward which it would roll, the spider pulled the two rearward legs far under the cephalothorax to act as a prop, and then pushed upwards with the legs on the opposite side. Torsion of the pushing legs was evident in some sequences. Once the spider had reached a critical roll angle, gravity pulled it the rest of the way over. While some features were consistent from trial to trial, tarantulas appear to lack a stereotyped motor pattern for flipping over.