Sister, sister

Dimorphic carpenter ant workers at a nest entrance.

The fine hairs on these Argentinian carpenter ants (genus Camponotus)  gave then a pretty golden sheen.  I spent a while watching the workers of this colony.  Clots of dirt extracted by diggers in the nest can be seen scattered around the periphery of the nest entrance, and form a large ring a few centimeters out.  The ants didn’t approve of my looming camera lens and I caused a bit of commotion in the ranks.

Like other eusocial insects such as termites and bees, ants divide tasks up among members of the colony.  In this case the daughter ants of the queen can take several developmental paths.  The vast majority develop into infertile workers, which carry out tasks such as nursing the young, tending the queen, building and maintaining the nest, foraging for food, and defending the colony.  As with many ants, the workers of carpenter ants are polymorphic– they may develop into different body forms, specializing in different tasks.  The large, broad headed and strong jawed ants such as the one seen above standing guard over the nest entrance are called ‘majors’.  The smaller, more typical ants such as the forager seen to the left returning to the nest, are called ‘minors.’

Many people are familiar with the concepts of ‘soldier’ and ‘worker’ ants.  The reality is more complex.  Some types of ants do not have polymorphic castes, or have a continuous range of worker sizes from small to large.  In some species of ants, the larger ants do indeed function as soldiers, while in other species they are more like pack animals, specialized for carrying large amounts of food back to the nest.  In some types of leafcutter ants, the minors ride on leaf cuttings carried by majors and defend the large ants from attacks by parasitic flies.  Smaller minors tend to be the primary nurses, as in many types of ants the major’s large jaws makes brood handling difficult.  However, in probably the majority of ants, workers progress through tasks with age, with dangerous jobs outside the nest generally relegated to the oldest workers.

The concept of the eternally busy and hard-working ant is equally inaccurate.  For example, in the typical fire ant nest, workers will often spend half their lives or more as ‘reserves’ available to be called on for a variety of tasks but otherwise inactive surplus.

Ring of dirt around a Camponotus nest entrance.