Bionomical Observations on Tarantula-Hawks and Their Prey (Hymenoptera: Pompilidae: Pepsis)1

Abstract

At Portal, Arizona, a female Pepsis f. formosa (Say) was discovered at 9 PM dragging a paralyzed male tarantula, Aphonopelma chalcodes Chamberlin, and was kept under observation for 4½ hours. In the first half-hour the wasp spent 8 min in moving the spider a total distance of more than 15 m, 2 min in antennating its prey, and 20 min in selecting a nesting site. Digging operations, begun at 9:33 PM and still unfinished at 1:25 AM, were repeatedly interrupted to antennate the spider, to move it in various directions and for various distances (up to 137 cm), and once apparently to sting it in its thoracic venter. At 7:30 AM the burrow was found completed and camouflaged by the wasp. This burrow, at a 45° angle with the surface, was 54 cm in total length, ranged from 23 to 28 mm in diameter, was enlarged into an empty cavity 45×64×45 mm about midway of its length, and terminated in a nest cell 57×32×38 mm, located 35.6 cm below the ground level. The prey apparently was dragged backward into the cell, where it lay venter down, with legs extended forward, and with a Pepsis egg glued on the side of its abdomen. It was not packed in the cell with dirt, but the burrow was plugged for most of its length. In the laboratory the egg, still attached to the spider, had not hatched at the end of 9 days. Another female of P. f. formosa was observed to spend the night in the entrance of a burrow made by another wasp, Cerceris macrosticta Viereck and Cockerell, at the bottom of an excavation made, perhaps, by a rodent. Females of Pepsis thisbe Lucas were used experimentally to flush female tarantulas from their burrows. They did this by antennating the web over the entrance, by vibrating it with their front tarsi or by actually entering the burrow—sometimes with fatal results to themselves. P. mexicana Lucas was once seen to flush a female A. chalcodes, only to walk away and leave the tarantula standing over the burrow entrance. Odors emitted by the wasps may perhaps play an important role in this hunting behavior. The ability of Pepsis to flush tarantulas at will from their burrows may account in large part for their diurnal and offseason success in collecting both male and female prey; males are more readily available in the mating season, when they are out of their burrows and searching for females in the late afternoon or at dusk. Although with most pompilids the sequence of events begins with hunting, proceeds through paralyzation and transportation of the prey, excavation, and oviposition, and ends with closure of the burrow, this sequence may vary with different species of Pepsis or with different individuals of the same species. They may prepare the burrow first, or sometimes may utilize the burrows of their prey. Occasionally one may hunt and paralyze a tarantula, only to abandon it entirely, though a nest cell may be excavated for it and then closed without an occupant.