The silk caps of the pupae of the Oriental hornet (Vespa orientalis, Vespinae, Hymenoptera) were measured for spontaneous electric current flow as a function of temperature. The measurements were made in the dark, within a range of biological temperatures. A clear correlation was detected between temperature rise and the increase in electric current forming in the silk. Thus at the temperature associated with maximal current, namely, 28-31°C, the electric current reached hundreds of nAmp whereas at 5°C the current was merely dozens of nAmp. Interestingly, the temperature range associated with optimal currents is also identical to the optimal temperature extant in the hornet nest thus enabling proper development of the colony. In the Discussion section, an attempt is made to explain the thermoelectric mechanism in pupal silk and its contribution, as thermometer and thermostat, to thermoregulation of the individual pupae, each of which is an independent thermal unit. The thermoregulation here is compared with the mode of action of heating pipes in industry. For further comparison, silk cocoons of the silkworm Bombyx mori were also measured, but while the readings on silkworm silk were comparable to those on hornet silk, they were lower by one order of magnitude.