7.1.2. Investigating thermotactic behaviour
One approach to investigate the dynamics of the honey bees' winter cluster, for example, is to model honey bee thermoregulation. These modelling studies readily assume a direct uphill/downhill approach of honey bees towards a temperature optimum (Sumpter and Broomhead, 2000). Although studies on the location of sensory organs necessary for such a direct gradient ascent/descent were performed decades ago (Lacher, 1964), little is known about the proximate mechanisms of thermotaxis of honey bees in temperature fields. Early experiments in a so-called "temperature organ" (Fig. 9; Herter, 1924; Heran, 1952) have indicated that the outer two segments of the bee antenna are the most important locations for the temperature sense of the honey bee. However, such "temperature organs" are only a very rough approximation of the inner climate of a honey bee colony. They can only generate simple steep gradients in an almost one-dimensional environment. In contrast to that, the inner space of a honey bee colony is a complex three-dimensional structure and every comb the bees crawl on can be interpreted as a two-dimensional space.
Fig. 9. The classical temperature organ according to Herter. Bees move in a one-dimensional thermal gradient in the central tunnel (l = 53 cm) until they find the spot of their preferred temperature. To establish the gradient, the tunnel is heated by a hot water bath at the left side and cooled by ice contained in the box to the right. The thermometers at the back survey the gradient.