are social insects which form small to large colonies. A typical colony
contains an egg-laying queen and many adult workers together with their
brood (eggs, larvae and pupae). Workers are by far the most numerous
individuals in the nest. They are responsible for nest construction
and maintenance, foraging, tending the brood and queen, and nest defence.
While all workers
are female, they are sterile and do not lay eggs. Winged queens and
males are present in the nest for only a short period. Soon after emerging
they leave the nest to mate and establish new nests. Queens are generally
similar to the workers, differing primarily in having larger bodies.
In some species, fully winged queens are lacking and egg-laying is undertaken
either by typical workers or by individuals which are morphologically
intermediate between typical queens and workers (these are called ergatoid
queens). Males are generally about the same size as the workers or smaller,
and have smaller heads with large ocelli, very short scapes and small
mandibles. In many cases males look more like wasps than ants.
in a single nest can all be the same size or they can very greatly in
size. When all are of the same or a similar size they are said to be
monomorphic. In some cases the variation in size can be so extreme that
large workers are twice the size of small workers (figures right). If
variation between small and large workers is continuous, the workers
are said to be polymorphic. If there are only two distinct size classes
of workers, they are called dimorphic. Many of the polymorphic and dimorphic
species show allometry. That is, the heads and mandibles of the large,
or major, workers are disproportionally large when compared to those
of the small, or minor, workers.
workers are the most commonly seen caste, especially as they forage
on the surface of the ground or when they are disturbed under rocks
or other objects. However, in most species not all workers forage outside
of the nest. Ants show a strong division of labour, where different
workers perform different tasks within the nest, and in some cases the
specific tasks undertaken will depend on the age of the ant.
It is common
for young, newly emerged workers to remain in the nest and tend eggs,
larvae and pupae. As the workers age, they may shift their activities
away from tending brood and begin to undertake nest construction and
excavation. Finally, later in life they may become foragers, leaving
the nest to search for food. In contrast to this, some workers may perform
the same activities throughout their lives, or in other cases, all workers
may undertake all activities of the colony, performing any given activity
for a few days before switching to another. In many dimorphic and polymorphic
species, the size of the worker will influence its
For example, major workers may only be found in or near their nests
while only minor workers forage away from the nest.
and division of labour, combined with their well-developed communication
systems, has allowed ants to utilise their environment in ways approached
by few other animals.