In Bombus huntii only certain workers are responsible for heating up the nest. Photo: © KS Matz
Reading Bumblebees rely on specialists to keep the temperature in their nest always pleasantly warm: In each people, certain workers are responsible for the cooling and others for the heating, American biologists have observed. There is no representation here? If cooling or heating animals fail, the remaining must intensify their efforts to balance the temperature. Decisive for who takes which job seems to be the size of the insects, the researchers discovered. Bumblebees, in contrast to many other insects, are warm-blooded animals, meaning that they can actively heat their bodies through increased muscle movement and thus continue their daily business even in low temperatures. This feature also allows them to keep the eggs warm with their bodies and regulate the temperature in the nest. However, how the animals manage to maintain the nesting temperature practically always between 30 and 33 degrees Celsius has so far been unclear.

To investigate, Kathryn Gardner and her research colleagues have now tagged various workers from three peoples of the bumblebee Bombus huntii, which lives in the northwestern United States and Canada. They then changed the temperature of the nests by chilling them down to about 10 degrees or by heating them to above 38 degrees, observing the labeled animals. The result: at lower temperatures, certain female workers intensified the movements of their flight muscles, allowing them to produce more heat. As temperatures rose, they diminished those efforts and received additional support from other female workers, who used their wings to fan cooling air into the nest.

The number of heating insects was always about the same, the researchers observed. Even if some of the warmth-related animals were removed from the nest, no additional workers jumped in. As a result, the temperature dropped briefly, until the remaining had increased their heat production far enough to compensate for the loss. Interestingly enough, according to the scientists, it was not the biggest bumblebees that were responsible for the heat, but the smallest ones. "We do not know if the little animals can actually warm the nest better, or if the big ones avoid breeding for other reasons, " explains co-author Sean O'Donnell. The strong specialization of the individual workers is remarkable, because so far it had been assumed that the animals can exchange their jobs with each other.

Kathryn Gardner (Cornell University, Ithaca) et al .: Behavioral Ecology and Sociobiology, Online Preliminary Publication, DOI: 10.1007 / s00265-006-0309-7 ddp / science.de? Ilka Lehnen-Beyel advertisement

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