Estimation of thermal constants: the importance of using equilibrium temperature rather than ambient temperature demonstrated with hoverflies (Diptera, Syrphidae, genus Eristalis).

Water evaporation has a marked effect on the passive rates of body temperature change of eristaline hoverflies. It results in the equilibrium temperature of these flies being significantly lower than ambient temperature. Different values for the cooling and warming constants are therefore obtained depending on whether equilibrium or ambient temperature is used as the baseline. Hence, care must be taken when estimating these constants with all animals, especially those of moderate to high permeability. It is recommended that equilibrium temperature be used in such situations. Evaporative cooling is probably also responsible for cooling constants being higher than warming constants in this and other studies.