Exploitation of floral signals by crab spiders (Thomisus spectabilis, Thomisidae)

Flowers exhibit characteristics through which they exploit the sensory biases of pollinating insects, and both signaler and receiver benefit from this interaction, either through reproductive service or food reward. However, the preferences of pollinators for certain flower traits such as color or odor might be exploited by predators that target pollinating insects. Crab spiders, Thomisus spectabilis, position themselves on flowers to prey on pollinators such as honeybees, Apis mellifera. We gave both honeybees and crab spiders the choice between two randomly chosen white Chrysanthemum frutescens, including olfactory signals in one experiment and excluding odor in a second experiment. When olfactory signals were included, crab spiders and honeybees clearly preferred the same flower out of a pair. However, agreement level was at chance in the absence of olfactory signals. We also analyzed the visual flower characteristics that might influence the decision of the animals. Neither the size of flowers (diameter of flower and diameter of reproductive flower center) nor the reflectance properties (receptor excitation values in ultraviolet, blue, and green; overall brightness) influenced the choices of crab spiders and honeybees. Therefore, odor seems to be the floral signal that bees use to identify high-quality flowers and that crab spiders exploit to encounter honeybees.