Male chimpanzees try to control the movements of fertile females.

Unofficially, everyone thinks I've a secret pond out here full of fertile females.

The fertile females are mature enough to reproduce when they're two and a half or three years.

Why shouldn't they be allowed to benefit by contracting with a fertile low-income female to carry their child for a fee?

The eggs hatch in the spring and have been estimated to number as high as 200 per fertile female.

She is the only fertile female, and deposits all the eggs from which the other bees are produced.

Another form of worker-based policing is aggression toward the fertile females.

And each fertile female can theoretically produce a new litter, averaging 10 young, every 45 to 50 days.

Queen - the fertile female which starts the colony and lays eggs.

New queens - fertile females, each of which, once fertilized, may start its own nest in the spring.