Analysis of Heat Transfer in Vanessa Butterflies: Effects of Wing Position and Orientation to Wind and Light

Abstract

Many diurnal lepidoptera rely on solar basking to achieve elevated thoracic temperature. We examined the effects of wind, radiation, body orientation, and wing position on the thoracic temperature excess ($T_{ex}$) of a typical basking butterfly, Vanessa cardui (Lepidoptera: Nymphalidae). Dried, thermocouple-equipped butterflies were subjected to a variety of combinations of wind speed, wind and light orientations, and body positions. In most combinations of wing position and wind velocity, $T_{ex}$ was maximized when the animal faced directly away from the wind, regardless of light orientation. Conversely, $T_{ex}$ was usually minimal when the butterfly faced directly into the wind. The exceptions to this general pattern consisted primarily of specimens with closed wings held perpendicular to incident radiation, whose $T_{ex}$ appeared to be more sensitive to light angle than to wind angle. We observed no consistent effect on $T_{ex}$ of opening or closing the wings under a given ambient light and wind r...