Visual signals invisible to humans may be used by spiders to manipulate prey behavior and increase capture success, but the precise nature of these signals has been unclear. In the January 23 Nature, Astrid M. Heiling and colleagues at the University of Vienna, Austria, show that an Australian species of crab-spider (Thomisus spectabilis) manipulate ultraviolet flower signals to attract more insects (Nature 421:334, January 23, 2003).

Heiling et al. examined the mechanisms employed by T. spectabilis to interfere with floral signals on the white daisy Chrysanthemum frutescens. They observed that T. spectabilis — which is well camouflaged on the petals at human visible wavelengths — was strikingly clear to ultraviolet-sensitive insect prey. The contrast of the spider against the petals made the flowers more attractive to pollinators — such as the honeybee Apis mellifera — who use UV markings to identify suitable flowers.


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