Thermal gains through collective metabolic heat production in social caterpillars of Eriogaster lanestris

We investigated thermal characteristics of aggregations of social, tent-bui lding caterpillars of the small eggar moth Eriogaster lanestris (Lepidopter a: Lasiocampidae). The highly synchronous behavior of individuals of the co lony has important consequences for their thermal ecology. Air temperature in the tent fluctuates according to the caterpillars' activity: air tempera ture slowly rises about 2.5-3 degrees C above the surroundings when caterpi llars aggregate in the tent after feeding and decreases rapidly when the la rvae leave the tent. Thermal energy can be stored for a few hours when ambi ent temperature drops. Experiments show that metabolic heat production suff iciently explains this effect. As even minor additional heat gain may reduc e developmental time, aggregating in the tent may thus confer selective adv antages under overcast weather or at night, when behavioral thermoregulatio n through basking is not possible.