Risk assessment by grasshopper mice (Onychomys spp.) feeding on neurotoxic prey (Centruroides spp.)

Predators should benefit from assessing the risks posed by prey that differ in their dangerousness. Assessment might come at any phase of the predatory sequence: search/recognition, pursuit/attack and handling/subjugation. Grasshopper mice are voracious carnivores in North American deserts, feeding almost exclusively on arthropods. In certain regions, grasshopper mice co-occur with extremely neurotoxic bark scorpions, whose sting can prove lethal to vertebrates. We presented three different prey items to wild-caught grasshopper mice at several field sites in the southwestern U.S. The three items, listed in increasing order of dangerousness, were: laboratory crickets, Acheta domesticus, having few or no defences; two sister species of Vaejovis spp., a non-neurotoxic genus of scorpion; and two sister species of toxic Centruroides. Grasshopper mice made no distinctions among the prey in either the recognition or pursuit phases of the encounter, attacking crickets and both genera of scorpions with little hesitation. There were, however, significant differences in how the mice handled the three different prey types, with Centruroides requiring significantly more effort to subdue. The difficulties that mice had in dispatching Centruroides were not related to the neurotoxic components of these scorpions' venoms, to which the mice are resistant. Instead, the difficulties appeared to result from other constituents of Centruroides' venom that cause intense, short-term pain.