Arachnids as systems for robophysical study

Arthropods in the class Arachnida (inclusive of 8 orders and over 100,000 species) demonstrate suites of remarkable adaptive biological features, which lend themselves to robophysical study. The arachnid body plan is two body sections and four pairs of jointed walking legs extending from the anterior body section. In addition, they have a fifth set of leg-homologs in front of the legs that serve as sensors, grabbers, or sex organs. The running mechanics and leg features of spiders have been modeled and tested using the rHEX and RiSE robotic platforms, respectively, but a range of opportunities for study remain. Arachnids, with eight legs and a tendency to autotomize them when in danger- make an ideal study system for leg redundancy and flexibility in limb usage after loss. Solifugae (“wind-scorpions”) have adapted to running on flowing substrates at steep angles; the mechanism for this is unknown. Finally, spiders make prey traps (webs) using small, variously spaced protein strands. Each of these systems suggests hypotheses of selection leading to optimization, but empirical data are ambiguous. We suggest that for these varied arachnid adaptations, robotic systems can be used to better test- and possibly optimize- key mechanisms of these systems and their analogs.