File:Caste sizes.jpg

In most species of ants, all of the workers are the same size. The workers of these species choose what jobs to do based on their age. Young workers do jobs inside the nest while older workers do the more dangerous jobs outside of the nest. However, a few ant species (less than 15 percent) can make different-sized workers, an ability known as size polymorphism. The leafcutter species shown here has a range of sizes among its colony members.

In this expanded image, two very large queens can be seen on the far right. In the top middle is the soldier, which is small compared to the queens, but large compared to the other workers. Examples of the smaller castes (guards, nurses, foragers, etc.) are shown to the left.

Having different-sized workers is great for the colony because large workers can specialize in big jobs and tiny workers can specialize in small jobs. But how do some ants get so large in these species?

Unlike us, an ant does not grow throughout its life. An ant hatches out of its egg looking like a tiny, worm-like jellybean. They eat and grow until they pupate, a process during which their body changes and they come out looking like an adult ant. It's similar to the change that caterpillars go through to become butterflies. An ant’s size after pupation will be the same for the rest of her life. This means that a very small nurse ant can be older than the largest soldier ant in the colony. An ant can grow to be big or small depending on how it was treated and what it was fed as a larva.

Image by Sarefo and modified by GameKeeper.