E51 Body thermal exchange

Topic

The heat exchange of an ectothermic insect is generally dominated by the net difference between its metabolic heat production and the heat losses—via convection, radiation, and evaporation—accounted for in the comprehensive energy balance model.

This energy balance, based on the first law of thermodynamics, establishes the differential equation that governs the insect's body temperature over time.

This small insect has a remarkably low Biot number; consequently, its internal temperature is virtually uniform—a condition known as the lumped capacitance approximation, which simplifies the thermal analysis.

Convective heat loss is the dominant factor for an insect in motion or in a ventilated environment, whereas radiative heat loss—modeled separately—is significant primarily within the infrared spectrum.

Wasps and some butterflies regulate their thoracic temperature by pre-warming their flight muscles through shivering before takeoff, thereby increasing metabolic heat production—specifically within the thorax, which is also modeled as an elastic resonator. If the wasp shivers its flight muscles more intensely before takeoff, its metabolic heat production increases further. Thus, given the balance between metabolic heat production and heat loss via convection, radiation, and evaporation—the factors with which this model began—the insect's final equilibrium temperature is determined by the specific body temperature at which it stabilizes under constant conditions. If the insect's metabolic heat production exceeds the heat loss via convection, radiation, and evaporation to an even greater degree, the resulting final equilibrium temperature will consequently be higher.

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