SPIDER SIZE AND LOCOMOTION ON THE WATER SURFACE (ARANEAE, PISAURIDAE)

Abstract

Abstract Newly emerged fishing spiders, Dolomedes triton (Walckenaer 1837), can achieve rowing velocities as high as those of adults despite an approximately 600-fold difference in mass (1.7 mg vs. 1.1 g). In contrast, when velocity is measured in relative terms (body lengths/sec), small spiders move much more rapidly than adults, with Vrel ∝ mass−0.31. This surprising performance of very small spiders can be attributed both to their very high stride frequency (fs ∝ mass−0.43) and to the high angular velocity of their propulsive legs (ω ∝ mass−0.33). Calculations of leg tip velocities, based on measurements of both angular velocities and leg lengths, reveal that maximum leg tip velocities are achieved by spiders of about 33 mg, nineteen times more massive than the smallest spiders we tested. Some very small spiders perform conspicuously and consistently less well than do others of the same size. A detailed dissection of the motion of these underachievers reveals that a disproportionate amount of their row...