Butterflies are noted for their expansive wings that typically cover more area than the rest of their body. Although the large area could potentially collect heat, studies have shown the opposite to be true. Wings shade the abdomen and keep the butterfly cooler in the sun. In a 1980 study, John Rawlins found that male black swallowtails, Papilio polyxenes, changed their body position in response to temperature. When cool, the males hold their abdomen up so the sunlight shines directly on the abdomen and warms the body. When warm, the males keep the abdomen in the shade of the wings.
Insects are poikilothermic (cold-blooded), but they do have ways of regulating their body temperature. Thermoregulation is necessary because the mechanical properties of the thorax change with temperature. Rawlins found that male black swallowtails cannot fly unless the thorax temperature is 24 C or above. Vigorous flight only occurs above 28 C. In ambient temperatures between 14 and 22 degrees Centigrade (57 – 72 F), swallowtails will regulate the thorax temperature between 28 and 32 degrees Centigrade (82 – 90 F).
Swallowtails primarily thermoregulate by basking in the sun. Moths that fly at night, cannot bask in the sun and will beat their wings to raise the temperature of their thorax (shivering). Swallowtail butterflies only generate limited heat by shivering. Swallowtails do not fly when the sun is not shining, thus have less need for ways to warm the body other than basking in the sun.
Male Black Swallowtail Butterfly Drinking Nectar
