Facultative Endothermy
Many insect species are able to maintain an abdominal temperature above the ambient temperature using exercise. These are known as facultative or exercise endotherms. The honey bee, for example, does so by contracting antagonistic flight muscles without moving its wings. This form of thermogenesis is, however, only efficient above a certain temperature threshold, and below about 9–14 °C (48–57 °F), the honey bee reverts to ectothermy.
Read more about this topic: Endotherm