Transpiration is relatively independent of body temperature, up to some point. Water is lost from the body surface at a constant, but rather low, rate through a broad range of temperatures. At some temperature the cuticle reaches a temperature point called the transition point. This point varies from insect to insect, depending upon the chemical composition of the hydrocarbons and waxes in the epicuticle. Insects living in hot, arid habitats tend to have wax layers with higher transition temperatures than do insects living in cooler or more humid habitats.
Some insects have two transitions points.
Water loss from the body surface is held to a low rate by the oriented wax layer on the outside of the cuticulin. When the temperature of the cuticle rises to such a point that the van der Waals forces holding the wax molecules together are broken, the molecules move slightly apart and water is allowed to escape. Below the transition temperatures the wax molecules are close together, and at a slight angle so that water loss is restricted. At temperatures above the the transition point, the molecules part, which usually leads to a quick and probably pleasing and comfortable death due to dehydration. Another important avenue of water loss in terrestrial insects is from the respiratory surfaces.