Abstract
Bombus vagans forages for nectar at 5°C in shade and at 31°C in sunshine. The production of heat while the bumblebee is on flowers, at ambient temperatures below 24°C, helps to maintain a thoracic temperature that is near the minimum for flight between flowers. However, at ambient temperatures above 24°C the thoracic temperature is no longer regulated at 32° to 33°C and rises.