Some Consequences of the Shape and Orientation of 'magnetic' Termite Mounds.

Abstract

The possible thermoregulatory significance of north-south orientation of "magnetic" termite nests was investigated. Measurements in the nest during three days in early winter showed that a temperature plateau developed between approximately 1000 and 1730 hr each day, at 33-35C. This contrasted with night time temperatures as low as 13-15°C. The nest was then sawn off at the base and rotated into an experimental east-west orientation. In this situation no plateau was detected and temperatures rose to daily maxima of 40-42°C. Apparently north-south orientation of the wedge-shaped mound affords rapid warming in the morning, avoids excessive heating by presenting a low profile to the midday sun, and maintains the warmth of the nest late into the day. This finding confirms and amplifies earlier hypotheses. Thermal gradients within the nest support the idea that convection currents may aid air circulation. An hypothesis is advanced to account for the evolution of the unusual wedgelike shape of magnetic nests. This shape has a larger surface area-mass ratio than a spheroidal one and may be an adaptation to facilitate gas exchange.