Mimicry in Terrestrial Locomotion

Locomotory behavior is particularly effective in fooling or confusing predators, and again there are many anecdotal descriptions of across-taxa similarities. For example, although they look quite dissimilar, the Brazilian long-horned grasshopper Scaphura nigra mimics the fossorial wasp Pepsis sapphires; they both have the habit of running short distances with expanded wings [46]. The wasp adopts this behavior when hunting, but it is uncharacteristic behavior for a grasshopper. The grasshopper also has antennae modified to make them look shorter and more like those of the wasp [35]. Hoverflies of the genus Xylota, which resemble wasp species of the families Ichneumonidae and Pompilidae, also show similar running behavior when they are foraging on leaves; they both move in fits and starts with frequent changes in direction.

Nymphs of the bug Hyalymenus (Hemiptera: Alydidae) enhance their mimicry of ants by constantly agitating their antennae and adopting zigzag locomotion [48]. First instar nymphs of the stick insect Extatasoma tiaratum (Phasmidae) also adopt uncharacteristic behavior, running around very rapidly and looking very much like ants (personal observation).The ant-mimicking behavior of salticid spiders mentioned above, which only use six legs when running about with ants, has been the subject of some study [13], but the kinematics of the leg movements has not been investigated; it would be interesting to see if the gait of the two organisms is similar. Both clubionid and salticid spiders adopt a zigzag running gait to supplement their antennal deception [49], and some myrmecomorphic jumping spiders show a reluctance to jump unless seriously threatened [50]. Others show more specific mimetic behavior: Synemosyna spp. tend to walk on the outer edge of leaves like its model species of the genus Pseudomyrmex [51].

Wickler [13] described an example of superb morphological mimicry between a grasshopper and two beetles that requires the grasshopper to occupy two different niches at different stages in its life. Tricondyla, a genus of tiger beetles of varying size and with a powerful bite, scurry about on the forest floor in Borneo. The grasshopper Condylodera trichondyloides occurs in the same locations and looks very much like Tricondyla even in its mode of running. It seems to have compromised its jumping ability by evolving shorter hind legs, though once again the kinematics of its locomotion and the gait it adopts have not been investigated. Beetles pupate and thus do not alter their size in adulthood unlike grasshoppers, which pass through a number of moults, increasing in size each time. Young Condylodera grasshoppers are smaller than their model tiger beetle and do not live on the forest floor. Instead they live in the canopy, occurring in tree flowers along with another beetle Collyris sarawakensis that they resemble in size and color. So for many Batesian mimics, it is important that they are in the right place at the right time.

Many lycid beetles (Coleoptera: Lycidae) are considered to be models for Bate-sian mimics (although see the comments by Brower [10], who challenged the evidence for unpalatability). These have aposematic coloration on the elytra, gregarious habits, and sluggish behavior [52]. Two European wasp-beetles, Strangalia spp. and Clytus arietis are black and yellow, suggesting that they mimic social wasps. Strangalia is similar in color to a wasp but moves in a characteristically slow beetlelike way whereas Clytus differs in not having such a close resemblance to a wasp and adopts uncharacteristic active, jerky movements that are thought to resemble hunting wasps, suggesting that it is a Batesian mimic [3]. It may be that the mimic that is less convincing in terms of appearance is enhancing its mimicry by adopting wasplike behavior whereas the more-convincing mimic does not need to because it is convincingly unprofitable. The idea that "poor" mimics may enhance their mimicry by adapting their behavior has also been suggested for some hoverflies that mimic honeybees [53,54].

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