No abstract

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The integrity of social insect colonies is maintained by members recognising and responding to the chemical cues present on the cuticle of any intruder. Nevertheless, myrmecophiles use chemical mimicry to gain access to these nests, and their mimetic signals may be acquired through biosynthesis or through contact with the hosts or their nest material. The cuticular hydrocarbon profile of the myrmecophilous salticid spider Cosmophasis bitaeniata closely resembles that of its host ant Oecophylla smaragdina. Here, we show that the chemical resemblance of the spider does not arise through physical contact with the adult ants, but instead the spider acquires the cuticular hydrocarbons by eating the ant larvae. More significantly, we show that the variation in the cuticular hydrocarbon profiles of the spider depends upon the colony of origin of the ant larvae prey, rather than the parentage of the spider.

Many species of orb-spinning spiders construct silk decorations within the structure of the orb-web. The evolutionary significance of these decorations is poorly understood, but the silk decorations of many species reflect UV light, suggesting that they may function to attract insects. In these species, relatively more silk decoration may be required under dimmer light conditions in order to maintain a constant UV-reflecting signal, and hence level of insect attraction. We investigated experimentally whether the orb-spinning spider Argiope aetherea adjusts the amount of silk decoration added to the web according to light conditions. Consistent with the prey-attracting function, we found that spiders adjusted the quantity of silk decoration to their webs, adding more silk decoration when the web was located in dim light rather than bright light.

The salticid spider Cosmophasis bitaeniata is a myrmecophilic associate of the green tree ant, Oecophylla smaragdina. The abundance of C. bitaeniata on a tree or shrub is positively correlated with the number of nests of O. smaragdina on that vegetation. Experiments with captive spiders confirmed that the spiders prey on the larvae of their highly territorial and aggressive ant host, typically by removing the larvae from the mandibles of minor workers. C. bitaeniata avoids direct contact with major workers of O. smaragdina in daylight, but congeners elicited higher activity levels of major workers than either nestmate workers or C. bitaeniata. These data suggest that C. bitaeniata may be an exploitative chemical mimic of its host.R . A A l l a n , M . A . E l g a r S a l t i c i d s p i d e r p r e d a t i o n o n g r e e n t r e e a n t s R . A . A l l a n a n d M . A . E l g a r Z O 0 0 0 8 8