Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
Arachnids in general do not have a well-developed olfactory sense, but in whip spiders (Amblypygi), the first pair of legs are modified from walking appendages into sensory structures. These antenniform first legs are extremely elongate and are covered with hairs that, from their structures, appear to be mechanosensory and chemosensory. Some of the hairs are multiporous, resembling the olfactory sensilla of insects. The general olfactory capabilities of these arachnids were studied using electrophysiological techniques. Electrolegograms (ELGs) were recorded from both sexes of the whip spider Phrynus parvulus. Responses to 44 chemicals representing different chain lengths of acids, aldehydes, alcohols, and acetates, along with a variety of terpenes, monoterpenes, and ring compounds were examined. Dose response curves were generated for carvone, guaiacol, hexanal, methyl salicylate, benzaldehyde, caprylic acid, and linalool. Guaiacol, benzaldehyde, and hexanol elicited the greatest responses and no differences were detected between the sexes. Across the functional groups, carbon chain lengths of 5 and 6 generated the greatest responses and all the monocarboxylic acids and ring compounds elicited responses. Eighty percent of the chemicals tested elicited responses, suggesting that amblypygids have a very well developed olfactory sense and are sensitive to a wide range of volatile compounds that might occur in the environment.