Ant

F

Aphid-Tending Ants

Numerous species of ants collect a sweet substance called honeydew that is excreted by various tiny insects, including aphids, mealy bugs, and scale insects. The insects most commonly used for this purpose are aphids, which pierce plant tissues to suck up juices from a plant. Among some of these ants, workers leave their nests regularly to watch over groups of aphids and protect them from predators. In some instances, these ants construct shelters out of soil or carton to shield the aphids from the environment.

Worker ants stroke the aphids with their antennae to induce them to release drops of honeydew. The ants then transfer this honeydew through trophallaxis to another group of workers, who carry it back to the nest and share it with nest workers. Individual workers may spend days or weeks among the same group of aphids.

G

Honeypot Ants

Certain species of ants produce individuals who serve as living food containers, called honeypots. During seasons when the colony has access to abundant nectar and honeydew from plants, aphids, or other insects, worker ants feed these liquids to young adult workers called repletes. Over time, the crops and gasters of the repletes become so full that these ants are unable to walk. The repletes become living storage tanks and simply hang from the roof of specially designed storerooms. When food is scarce, the repletes regurgitate their stored liquids back to nestmates through trophallaxis. A replete is typically stretched so full with liquid that if it falls from its hanging place it may burst open and die.

Honeypot ants occur most often in semi-arid zones where some method of food storage is needed to sustain colonies during times of the year when food is scarce. Ants differ from their hive-making relatives, the honeybees, in that they cannot create waxy structures for storing liquid foods, so they use their bodies for this purpose.

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H

Acacia Ants

Many types of ants have evolved mutually beneficial relationships with particular types of plants. An example is the relationship between acacia ants of the American tropics and some species of acacia trees. The trees provide hollow thorns that the ants use as nests. In addition, these trees have nectar glands that provide the ants with sugary food, and their young leaves have nutritious attachments that the ants feed to their larvae. In return, these aggressively stinging ants protect the acacia from insect and vertebrate enemies.

I

Slave-Makers and Social Parasites

Many species of ants exploit the labor or resources of other species of ants. Slave-making ants steal pupae from the nests of neighboring ants of a different species. When the pupae emerge as adult workers in the slave-makers’ nest, they regard that nest as their own and embark on a life of labor for the ants that captured them.

Some species of ants, commonly called Amazon ants, cannot survive without slaves. These ants have sharp mandibles that are better adapted for puncturing enemies than for nursing larvae or obtaining food. Amazon ants rely on slaves to forage for food, dig and maintain the nests, tend the young, and feed adult members of the colony through trophallaxis. Experiments show that when Amazon ants are separated from their slaves, they starve to death even if food is present.

Some ants are considered temporary social parasites. A newly mated queen of one of these species may enter the nest of a different species, kill the resident queen, and use the worker force to rear her own offspring. The new queen’s eggs develop into workers that gradually replace the host workers.

VIII

Evolution

Ants evolved from a wasp ancestor that hunted insect prey to feed its larvae in a nest. An important difference between wasps and the earliest ants was the presence of several generations in the same nest, which allowed cooperation to evolve. Increasing cooperation essentially resulted in a wingless worker caste and winged queens.

The oldest known fossil ants are 92 million years old. Preserved in amber, these fossil ants were discovered in 1998 in New Jersey. These ants, which lived during the Cretaceous Period (138 million to 65 million years before present) when dinosaurs flourished, had characteristics that are intermediate between wasps and today’s ants. One body structure that marks them as ants, however, is the presence of a metapleural gland in the alitrunk.

Ants gradually emerged as one of the Earth’s dominant insects. During the Cretaceous Period, ants made up only a small part of the insect life. By the Oligocene Epoch, which spanned from about 38 million to 24 million years ago, ants were far more abundant. By this time, about half of the modern groups of ants were already present.

The social evolution of ants is still in progress. Today, some species of ants show only little coordination within colonies, whereas others create highly cooperative societies that function as smoothly as a single organism. This diversity of social characteristics makes ants fascinating to study or observe.

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