Sized To Fit

Fire ant

Red Imported Fire Ant (Solenopsis invicta) sizes
Photo: Sanford D. Porter

Social insects can produce individuals that differ in size, features, function and behavior. Some social insects, such as the red imported fire, Solenopsis invicta  produce a continuum of worker sizes rather than discrete castes. The first offspring are the minims, the smallest ants produced. These ants must be fed entirely from the energy stores of the queen. The queen’s stores are limited and fire ants bet on a larger number of very small workers rather than a very small number of larger workers. The smallest workers must forage to feed the colony and begin excavation of the nest. In a full size colony, the majority of workers are small, with a substantial number of medium sized ants and a small number of large ants. The worker size as well as the age is related to specialization and division of labor.

Some harvester ant species have discrete casts that are specialized to preform tasks. Many seeds that they collect are hard and require powerful jaw muscles to crack. Muscle power is proportional to muscle size. The workers that specialize in cracking and grinding seeds must have enormous (for a harvester ant) heads to accommodate the large muscles. Seed cracking majors are expensive to produce. They are typically in low numbers and do not leave the safety of the nest. Foraging is left to smaller “Minors” that require less resource to produce. Foraging ants that venture outside the nest suffer a higher mortality from predators. By investing fewer resources to produce the foragers, the colony minimizes its losses to predation, while maximizing its food collection and production.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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