Giant honeybees shimmy in time to cool the hive
Researchers saw certain bees act as 'fanners' during the hottest part of the day. Amy Middleton reports.
Giant honeybees may keep their nest cool by jiggling in sync to mimic the inhale-exhale motion of a lung, thereby swilling fresh air around the hive, a new study says.
This bizarre method of bee-created "ventilation" is described in a paper published this week in the journal PLOS ONE.
Developed by zoologists from the University of Graz, Austria, the theory attempts to solve the mystery of how Asian giant honeybees (Apis dorsata) cool their nests, which are semi-spherical and constructed out in the open, leaving them exposed to harsh weather and high temperatures.
As well as building their nests in careful locations to maximise shade, researchers have previously seen lines of worker bees, five to seven bees deep, that cluster at the edges of the giant honeybees' single-comb nests.
This "bee curtain" contracts in cooler weather and widens in the heat.
The new research, led by Gerald Kastberger, examined the behaviour of bees in nests in Nepal. Using infrared detectors, the team noticed that cool nest regions emerged in the vicinity of the bee curtain and disappeared minutes later.
This suggests the bee curtain is capable of cooling temperatures within the hive, prompting what the team call the "ventilation hypothesis".
In other bee species, the fanning bees move their bodies in a particular alignment, directing air towards specific parts of the nest.
In the ventilation-style method, worker bees move in characteristic motions to create a contraction similar to the inhalation-exhalation of mammals' lungs as they breathe.
As the bees collect around the cooler areas of the nest, the paper suggests they stretch their limbs into the nest to create a swollen bee curtain, enlarging the space within the nest and thereby dropping the internal air pressure.
Next, the bees would then simultaneously relax their bodies, eliciting a sort of exhalation from within the nest.
"This would drive the bee curtain back to the comb by gravity, pressing the warm, residual, nest-borne and CO2-enriched air outwards through the diffuse leaking mesh structure of the bee curtain," the paper explains.
This is the first time such a cooling method has been described, and although it remains a hypothesis, the researchers say evidence is "strong" that an unknown method of ventilation is used by this species.