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Size 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 µ mass-0.31. This
surprising performance of very small spiders can be
attributed both to their very high stride frequency (fs
µ mass-0.43) and to the high angular velocity of their
propulsive legs (w µ mass-0.33). Calculations of leg
tip velocities, based on measurements |
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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 rowing
effort goes into vertical as opposed to horizontal work: the
ratio of vertical to horizontal work during rowing is 1.03
± 0.89 : 1 in normal fishing spiders and 5.18 ±
1.73 : 1 in the underachievers.
