Asian giant honeybees (Apis dorsata) may move in synchrony to ventilate and cool their nests during the hottest parts of the day.
Previous studies have shown that bees often insulate their nests with a “bee curtain” of five to seven layers of bees, as shown in this video. Most of the bees are aligned vertically, with heads up and abdomens down, but some point their heads away from the bee curtain, such as the bee in the middle of the shot.
A recent study found that the backward bees may serve as “fanners,” aligning their bodies to funnel air towards small areas on the nest surface that are cooler than neighboring areas in the bee curtain.
Gerald Kastberger and his team of researchers from the University of Graz, Austria, used an infrared camera and a vibrometer on several bee nests in Nepal to record changes in surface temperature and monitor slow horizontal movements of the bee curtain throughout the day.
Based on their observations, the researchers hypothesize that bees in the inner part of the curtain stretch their limbs against the comb to expand the inner nest area and lower internal pressure. This creates a vacuum effect that draws cool, fresh air through the funnels created by fanners. When the curtain bees relax, the nest interior contracts by gravity, pressing warm, stale air out through the meshwork of the bee curtain and completing the ventilation cycle.
While the authors did not directly observe the internal mechanism, they may have hit upon a previously unknown collective respiratory movement for nest cooling in giant honeybee colonies.
Research Article: Kastberger G, Waddoup D, Weihmann F, Hoetzl T (2016) Evidence for Ventilation through Collective Respiratory Movements in Giant Honeybee (Apis dorsata) Nests. PLoS ONE 11(8): e0157882. doi:10.1371/journal.pone.0157882
Video Credit: Kastberger et al. (2016)