Why are so many bumblebees male?

Bumblebees don't seem to know that they're supposed to be mostly girls instead of guys.

Female bumblebee workers hatch from fertilized eggs, while males develop from unfertilized eggs. Geneticists calculate that female workers tending the young share, on average, 75 percent of their genes with their sisters but only 25 percent with their brothers. Evolutionary theorists have predicted that such species would not favor males. Yet, Bombus terrestris bees raise some 13 sons for every daughter.

Researchers at the University of Amsterdam now report measurements from laboratory bee colonies that may help explain the mystery. Females need three times the food that males do, report Madeleine Beekman and Pam van Stratum. In tough times--most of the time in the real world--colonies do better investing more in the "cheaper" sex.

The researchers also expand on previous calculations indicating that a key factor in male predominance is the bumblebee male's tendency to mature before the female. The males may emerge first for the species on the whole, but the Dutch researchers found that females matured before males in 18 of the 41 well-fed laboratory colonies. Overall, the researchers argue in the August 22 Proceedings of the Royal Society Of London B, a mix of colony types constitutes a stable world where most bumblebees are guys.