Thermoregulation by the Black Swallowtail Butterfly, Papilio Polyxenes (Lepidoptera: Papilionidae)

Male black swallowtails, Papilio polyxenes, regulate thoracic temperatures in the field by behaviorally changing abdomen position, wing position, orientation to the sun, perching duration and perching height. At relatively low ambient temperatures (<14°C), postures with abdomens raised above the flattened wings were associated with long periods of perching relatively to the ground. Under relatively high ambient temperatures (>22°), postures with abdomens lowered in the shade of the wings were associated with shorter perch durations, greater flight frequencies, and higher perch heights. Between 14° and 22° ambient, thoracic temperatures were regulated between 28° and 32°. Shivering is not capable of elevating temperatures above ambient as much as basking alone does, and is seen only in disturbed individuals under conditions too cool for flight. Overheating due to metabolic heat production in flight is avoided by gliding or soaring with reduced wingbeat frequency. Swallowtails survive air temperatures above 50° for 30—min intervals in water—saturated air, but die above 46° at lower humidities. Swallowtails survive cooling to below 0°. Thoracic temperatures above 24° are apparently necessary for flight, and vigorous flight occurs only when thoracic temperatures exceed 28°. Thoracic—abdominal temperature differences were greatest at low ambient temperatures where thoracic temperatures necessary for flight are difficult to attain or maintain. At low ambient temperatures, decreased transfers of heat from thorax to abdomen via hemolymph circulation are associated with raised abdominal postures. At higher ambient temperatures, increased circulatory exchange between abdomen and thorax (augmented by abdominal contractions and a lowered abdomen) serves to dissipate heat from the thorax, especially when the abdomen is shaded by the wings.