Strategies of thermoregulation and foraging in two vespid wasps,Dolichovespula maculata andVespula vulgaris

Summary D. maculata, the white-faced hornet, stabilized (regulated) thoracic temperature (T _Th) over wide ranges of ambient temperature (T _a), whileV. vulgaris, the common yellowjacket, regulatedT _Th poorly. The hornets also maintained a higherT _Th than the wasps, sometimes heating 38°C aboveT _a. Attacking individuals of both species had higherT _Th than those either leaving or returning to the nest from foraging. The hornets, who are primarily hunters of live prey, showed peak activity near dawn, and they were as active atT _a=2°C as at 20°C. Being able to regulate theirT _Th and fly at the lowT _a should enhance their ability to capture small insects that are usually torpid at theseT _a. The yellowjacket wasps, on the other hand, who are scavengers as well as hunters, did not leave the nest at 2°C; their activity decreased greatly with decreasingT _a. Differences in the foraging technique of the two vespids may be related to their different abilities to thermoregulate.