Sleep may significantly define the behavior, ecology and evolution of animals. Widely acknowledged to exist across most of the vertebrates, sleep is being examined in a growing number of invertebrate species as well, including fruit flies (Drosophila melanogaster), honey bees (Apis mellifera), crayfish, and cuttlefish. Sleep's diagnostic characters include specific posture and immobility expressed periodically and for extended bouts. Sleep is easily reversible, increases an organism's arousal threshold, and is internally controlled (i.e., homeostatically regulated).
We experimentally tested colonies of paper wasps (Hymenoptera: Vespidae: Polistinae), primarily Polistes flavus (Cresson, 1868), for behavioral and physiological signs of sleep. Observational studies of caged wasps preceded experiments testing circadian metabolic rates (carbon dioxide production), arousal thresholds, behavior-dependent thoracic temperatures, and the existence of a homeostat regulating sleep. Wasps exhibited a specific, prone posture primarily during extended, recurring and rapidly reversible periods of relative immobility. Inactive periods began one hour after dusk and lasted until several hours after dawn. Although they did not show an expected sleep rebound following sleep deprivation, wasps responded with increased rates of return to the immobile state as the night of disturbance progressed, and maintained their circadian immobility in spite of a two day absence of light. Wasps also experienced decreased thoracic temperatures when immobile.
Results from the suite of sleep signs support the hypothesis that P. flavus wasps exhibit a sleep state, opening up prospects for studying social aspects of sleep in paper wasps.
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