INSECT societies are normally considered to be fairly rigid affairs, but now
two Canadian biologists have discovered that a species of bee changes its social
structure depending on the weather. The bees are also the first social insect in
which workers have been found to breed.
The social sweat bee, Halictus ligatus, is found all across North
America. A long-lived queen and up to a dozen chocolate-brown workers live
together as a colony. The bees live in holes in the ground, which are lined with
cells for the eggs.
Miriam Richards of Brock University in St Catharines, Ontario, and Laurence
Packer of York University in Toronto, Ontario, found that the weather affects
the size of the offspring, with smaller individuals hatching in cool, rainy
periods. 鈥淲e could have predicted that,鈥� says Richards, 鈥渂ut what we didn鈥檛
expect was a change in social structure as well.鈥� The researchers found that the
bees鈥� behaviour changed. As the weather improved, worker bees began to act more
independently and less like cooperative social insects (Oikos, vol 77,
p 68).
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Richards and Packer believe this social rearrangement may actually be in the
queen鈥檚 interest. 鈥淚t made no sense until we discovered that if it was warm and
dry, the female workers laid eggs too,鈥� says Richards.
Even under the best conditions there鈥檚 a limit to the number of eggs a queen
can produce in a given time, they point out. By having daughters which breed,
she increases the reproductive capacity of the colony. 鈥淓gg laying by workers
must fundamentally change how we view social insects鈥� organisation,鈥� says
Richards. In particular, she says, the discovery will force researchers to
question how 鈥渁ltruistic鈥� species reproduce.