Most Odonata probably exert some control over their body temperature. Such behaviour is favored by the high, variable temperature of their terrestrial habitat and by the fact that dragonflies are relatively large insects and thus exchange heat with the environment comparatively slowly. Different species may thermoregulate behaviorally by controlling the external heat load or physiologically by altering the amount of heat generated by or dissipated from the thoracic muscles. The former method is characteristic of perchers, which are usually in a situation that permits considerable modulation of intercepted solar radiation, mostly by postural adjustments. There is also evidence that some species may perch more frequently in the shade when ambient temperature is high. Fliers, by contrast, have little opportunity to control intercepted solar radiation but continually generate large amounts of heat during flight. They may alter their rate of heat loss by controlling haemolymph flow from the thorax or their rate of heat gain by changing the proportion of gliding vs. flapping flight. Some species combine behavioral and physiological modes of regulation. Adaptive geographic, seasonal, and inter-habitat variation occurs in the responses of dragonflies to temperature. Voluntary avoidance of high temperature seems most closely adapted to the thermal environment. Temperature responses and thermoregulatory ability also vary with age and sex. The effects of temperature on the activity patterns of Odonata and the adaptive significance of thermoregulation have yet to be rigorously demonstrated in most cases.