Small ants develop through a process of complete metamorphosis, passing through a larval stage equivalent to the caterpillar of other insects and the pupal stage. The larva is legless and is fed by the workers, a process called trophallaxis, whereby the worker regurgitates food it has eaten and digested. Adults also distribute food among themselves through this same process. Larvae and pupae need constant temperature to develop and are therefore transferred to different chambers according to their stage of development.
The caste differentiation is determined by the type of food they receive in the different larval stages and the morphological changes that distinguish each caste appear abruptly.
Ants communicate through a chemical process called pheromas. These message signals are more developed in ants than in other hymenopteran groups. Because ants spend their lives in contact with the ground, they leave a pheromone trail that can be followed by other ants. When a worker finds food, it leaves a trail on its way back to the colony, which is followed by other ants that reinforce the trail when it returns to the colony. Once the food is finished, the trails are not retraced by the returning ants and the smell dissipates. This behaviour helps the ants adapt to changes in their environment. When an established path to a food source is blocked by a new obstacle, the workers abandon it to explore new routes. If successful, the ant returns and marks a new trail for the shorter route. Successful trails are followed by more ants, each reinforcing it with more pheromone (the ants will follow the most strongly marked route). Their home is always located by reference points left in the area and the position of the sun; the ants’ compound eyes have specialised cells that detect polarised light, thus determining which direction to follow. Ants use pheromone for other purposes too. A crushed ant will emit a pheromone alarm, which, in high concentration, drives nearby ants into a rage of attack; if, on the other hand, the concentration is low, it attracts them. To confuse enemies, several species of ants also use pheromones, which make them fight among themselves.
Like other insects, ants can smell with long, thin antennae. The antennae have like elbows attached to the elongated first segment; and since they see in pairs – like binocular vision or stereo sound equipment – they get information about direction and intensity. When two ants meet, they touch their antennae and whatever pheromones are present provide information about the feeding status of each, which can lead to trophallaxis, i.e. one of them regurgitates food for the other. The queen produces a special pheromone that tells the workers when to start raising new queens.
The ants attack and defend themselves by biting or stinging, sometimes injecting chemical compounds into the attacked animal, especially formic acid.
From the stage when they are eggs to becoming adults, ants take between 6 to 10 weeks. Some workers can live up to 7 years, while queens can live more than 15 years.
Types of ants
There is a wide diversity of ants with different behaviours:
The worker ants, from South America and Africa, do not build permanent anthills and alternate between a nomadic life and the organisation of temporary shelters formed by the bodies of the workers. The societies reproduce either by nuptial flights or by splitting up the group. In this case, a group of workers separate and dig a nest to raise new queens. The members of each group can be distinguished by smell and usually attack other intruders.
Some ants attack other anthills, steal the pupae and raise them as workers, i.e. as real slaves. Some species, like the Amazon ant (for example, Polyergus rufescens), have become totally dependent on these slaves, to the point that without them they are unable to feed.
Honey-pot ants, on the other hand, create special workers, whose sole function is to store food in their own bodies for the rest of the group, remaining generally immobile, with large abdomens full of food. In dry, even deserted places in Africa, North America and Australia, these ants are considered a delicious “snack”.
Kelp ants (Oecophylla) build nests in trees by sewing leaves together to form worker bridges, which they then sew together with silk they obtain from larvae bred for the purpose.
The “leaf-cutter ants” of the genera Atta and Acromyrmex belong to the tribe Attini and live exclusively in the Neotropics and southern regions of the United States. Contrary to popular belief, the ants do not feed by ingesting the leaves they cut (but can ingest sugary exudates from these leaves). They feed on the fungus that they grow inside the anthill. They have several castes, with specific functions in the maintenance of the colony (workers, soldiers, garden workers) . Some cut and carry leaves, flowers and branches, others clean and defend the colony, others cultivate the fungus and care for the young, called larvae. The gardener ants cut the leaves and feed on the exuded sap. These leaves are carried to the inside of the anthill, where ants of another caste will grind them to produce a white fungus, the basis of their diet. The fungus supplies the food needs of all the ants that live exclusively inside the anthill, such as the larvae, and the queen. The queen lays her eggs for the duration of her life and through her offspring she perpetuates the colony. There are 14 known species of leaf-cutting ants of the genus Atta. Although well identified, the ants of the genus Atta and Acromyrmex, there are 11 other genera of leafcutters in the tribe Attini, totaling 13 genera of leafcutting ants. They are unique to South America.
Humans and ants
The house ant usually forms its nest in household appliances because of the temperature, and can often damage them. They usually inhabit hollow parts in the walls of houses. Ants come in handy because they can help exterminate other harmful insects and aerate the soil. However, they become a pest when they invade houses, gardens and crop fields. Carpenter ants destroy wood by drilling holes in it to nest.
Some species, called “killer ants”, tend to attack animals much larger than themselves, either to feed or to defend themselves. They rarely attack humans but can give very painful stings and, if they are numerous, can cause permanent damage or kill through severe allergy.
Cultural representations of the ant
From the point of view of its role in the imagery of Western culture, the ant represents work and cooperative effort, as well as aggressivity and the spirit of revenge. In parts of Africa, ants are considered messengers of the gods. Some North American Indian religions, such as the Hopi, consider ants to be the first inhabitants of the world. Others use ant bites in initiation ceremonies, as a test of endurance.