Collective control of nest climate parameters in bumblebee colonies

We examined two aspects of the social control of nest climate in bumblebee colonies: which parameters of nest climate bumblebees actively down-regulate by fanning and the dynamics of the colony response as colony size increased. Colonies of Bombus terrestris were exposed to an increase in carbon dioxide, temperature or relative humidity. We performed 70 temperature trials (six colonies), 58 CO₂ trials (four colonies) and four humidity trials (two colonies). An increase in CO₂ concentration and temperature elicited a fanning response whereas an increase in relative humidity did not. This is the first report of fanning in bumblebee colonies to control respiratory gases. The number of fanning bees increased with stimulus intensity. The colony response to a CO₂ concentration of 3.2% was comparable to the colony response to a temperature of 30°C. A marked fanning response occurred at 1.6% CO₂, a concentration never exceeded in a large field nest during a pilot measurement of 10 days. We investigated the colony response over a wide range of colony sizes (between 10 and 119 workers). The proportion of the total workforce invested by colonies in nest ventilation did not change significantly; thus, the number of fanning workers increased with colony size. Furthermore, as colony size increased, the dynamics of the colony response changed: colonies responded faster to perturbations of their environment when they were large (60 or more individuals) than when they were small. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.