Ant

I

Introduction

Ant, common name for members of a family of about 11,000 species of insects that live in highly organized societies called colonies. Ant colonies have elaborate social structures in which the various activities necessary for the feeding, shelter, and reproduction of the colony are divided among specially adapted individuals.

Ants belong to an order of insects called the Hymenoptera, a group that also includes bees, wasps, and sawflies. Some species of wasps and bees resemble ants in that they live in colonies and are therefore said to be social, but ants are the only hymenopterans in which every species is social. Ants are distinguished from other hymenopterans in that they have bent, or elbowed, antennae and an indented abdomen that forms a narrow waist.

Ant colonies range in size from a few members to many millions of members. Members of an ant colony typically fall into categories known as castes, each with a different role. The majority of colony members are female worker ants that are unable to mate. Worker ants do not have wings and perform most of the work of the colony, including searching for food, nursing young, and defending the colony against ants from other colonies. Queens are larger than worker ants and are the only females of the colony capable of mating. Queens are born with wings, which they break off after mating. They mate with winged male ants, later using the sperm from the mating to produce fertilized eggs, which hatch to produce more worker ants and a new generation of queens. Aside from mating with the queens, males play no social role in colony life and die soon after mating.

Ants live on landmasses all over the world, except for the permanently frozen Arctic and Antarctic, the coldest mountaintops, and a few islands. They flourish in soil, rotting wood, leaf litter, dead trees, and living trees in such varied habitats as mountains, deserts, swamps, and human homes. Ants are most abundant in the tropical regions. In the rain forests of the Amazon, for instance, ants are so numerous that their total weight is about four times the weight of all the area’s mammals, birds, reptiles, and amphibians combined.

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Ants play crucial roles in the ecosystems in which they live. Many species dig underground nests that have numerous openings and tunnels. Air and water pass into the soil through these passageways, making oxygen and moisture available to the roots of plants. Seed-eating ants remove seeds from plants and transfer them to underground storage chambers within their nests. This activity disperses the seeds, so that some of them can sprout in areas that are distant from the parent plants. Ants of many species feed on other insects, which may be either living or dead. In this way, ants reduce the size of some other insect populations and recycle organic matter. In turn, ants are a source of food for other animals, such as spiders, other insects, woodpeckers, and blue jays; toads, salamanders, and turtles; and anteaters, armadillos, and aardvarks. A few ant species are considered pests because they sting, invade human houses and yards, or damage wooden buildings.

II

Body Features

Most ants are between 2 and 10 mm (0.08 and 0.4 in) long. Some ants, however, are a mere 0.7 mm (0.03 in) in length, and others are nearly 3 cm (1.2 in) long. Like other insects, ants have bodies that contain three major segments: the head, the thorax, and the abdomen. Unlike other insects, however, the first segment of the ant’s abdomen is fused to the back of the thorax. For this reason, scientists use other terms to designate the second two segments of an ant’s body—alitrunk corresponds to the thorax, and gaster corresponds to the abdomen.

A

The Head

The shape of the ant head varies among different species; it may be spherical, triangular, egg-shaped, or rectangular. In all ants, at the back of the head is an opening through which nerves, the beginning part of the digestive tract, and blood pass into the alitrunk. At the front of the head is the mouth, which is associated with three appendages, or mouthparts. The mandibles, sometimes described as jaws, are long and broad, and they are serrated, or toothed, along their inner sides. Used for digging, carrying, collecting food, building nests, fighting, and cutting, the mandibles are probably the most important work tool that ants possess. The other mouth appendages are the maxillae, or lower jaws, used for chewing foods to extract liquids, and a tongue for sucking up liquid food. The mouthparts also have two pairs of slender palpi, segmented structures resembling small antennae, which play a role in tasting food.

Most ants have two compound eyes, which are made up of light-sensitive compartments called ommatidia. These compartments work together to generate an image in the ant’s brain. Some types of ants have three simple eyes, called ocelli, at the top of their heads. Ocelli can detect light, but they do not form images. Different species of ants vary in their ability to see: Some have well-developed sight, but others are entirely blind. Sight is of little importance to those ants that spend all or much of their lives underground.

Attached to the front of the head is a pair of flexible, segmented appendages called antennae, which contain organs of taste, smell, and touch. Each antenna is shaped like a human arm that is bent at the elbow. This antennae shape is an identifying feature of ants. Antennae are an ant’s main source of information about the world. When an ant is active, its antennae are in nearly constant motion—tapping the ground or vegetation, other ants, and food sources, or sampling odors from the air.

B

Alitrunk and Petiole

An ant’s head connects to the alitrunk. This middle part of the body bears three pairs of jointed legs, each of which ends in a claw. The legs are used not only for walking or running but also for more dexterous tasks, such as handling food. Each of an ant’s front legs contains two combs that the ant uses to clean its other legs and its antennae.

In males and young queens, the alitrunk contains two pairs of wings: a larger front pair and a smaller rear pair. During flight, the hind pair of wings is hooked to the rear edge of the front pair so that the two pairs function as a single unit.

Behind the alitrunk is the narrow petiole, a one- or two-segmented section that forms what appears like a waist. This slender body part helps ants to bend while passing through twisting underground tunnels. In all ants, the alitrunk contains a structure called the metapleural gland, which secretes an antiseptic chemical that destroys bacteria and fungi. Ants rely on this chemical to keep their moist underground nests free from microorganisms that might destroy eggs, larvae, pupae, or stored food supplies.

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