Biologist (Prof. Ehab Abouheif) has figured out that the ants themselves are determining how many in their colony become larger, soldier ants, depending on the need of the colony. Check out the news story here and the full research paper here.
When an ant colony is threatened the percentage of soldier ants in the colony can grow from 5% to 10%.
The colony doesn’t want too many of these big guys around because they use up a lot of resources, so they emit an “inhibitory pheromone” that actually controls how many big guys (soldiers) are produced. This pheromone controls the presence of rudimentary “wing disks” (wing placeholders), that actually restrict the size to which an ant will grow.
Read all about it here.