We’ve seen a lot of press about heater bees lately, but researcher Jurgen Tautz, explained this phenomenon in detail in his 2008 book, The Buzz about Bees. Using temperature-sensitive film, Tautz found that some bees are able to raise their body temperatures about 10 degrees C higher than normal bees by using rapid muscle contractions. Each of these bees then presses its thorax against the top of a developing capped pupa, keeping it warm.
He also found that the isolated empty cells commonly found in brood nests are used by heater bees. After warming their abdomens, some of the bees climb head-first into these cells where they remain about 30 minutes, or until their bodies drop back down to a normal temperature. A heater bee tucked down in one of the empty cells is even more effective at distributing heat to the developing pupae.
Temperature may determine roles
The most recent findings about heater bees reveal that they may actually be determining which pupae will perform which functions when they mature into adults. For example, pupae kept at 35 degrees C turn into foragers that search out sources of nectar and pollen, while pupae kept at 34 degrees C become “housekeeper bees” that perform chores within the brood nest such as feeding and cleaning.
Tautz speculates that using this technique, worker bees can assess the state of the hive, determine what types of bees are most needed, and then produce those types. This phenomenon seems less far-fetched when you realize that other species use temperature to influence developmental outcomes. Some fish, turtles, and crocodiles, for example, use temperature to influence the sex of their young. In these examples, as with bees, certain temperatures alter the course of development which yields different types of adults.
The value of empty cells
The findings about heater bees call into question some of our breeding practices. For a long time beekeepers have been selecting against queens who leave empty cells in the brood area, believing they are somehow inferior to queens who fill up every cell. Now we should reconsider. Perhaps the queens who leave empties are the superior stock, allowing plenty of opportunity for the heater bees to keep the brood warm and raise the kind of bees that are most needed by the colony.
Honey Bee Suite
BTW, for great pictures of heater bees taken with heat-sensitive film, check out the book!