Digestion time and reemergence in the desert grassland scorpion Paruroctonus utahensis (Williams) (Scorpionida, Vaejovidae)

Abstract

The desert grassland scorpion Paruroctonus utahensis spends most of its life in its burrow. During the active season, only about 5% of the individuals in a population appear on the surface each night. Individuals do not appear on the surface for several nights following a meal. To determine if physiological digestion time could account for this delay in reemergence after eating, I measured changes in oxygen consumption immediately following a meal. Oxygen consumption exceeded 125 μl O₂g^-1h^-1 just after completion of a meal, then dropped to normal levels (53 μl O₂g^-1h^-1) within 6 h. I also measured the interval between completion of the meal and subsequent defecation. All individuals defecated by 72 h following ingestion (median 12 h). In field enclosures, scorpions returned to the surface after a mean of 20.3 days (median=16) following a successful predation event. Lack of correspondence between estimates of physiological digestion time and the reappearance interval lead me to reject the idea of a long digestive pause in Paruroctonus utahensis. This conclusion lends support to the hypothesis that scorpions remain in their burrows to minimize exposure to predation.