Army ants: The world’s deadliest ants

Army ants also known as legionnaire and marabunta ants are aggressive ants that move in marching formations and kills anything in their path. The name army ant is used to refer to more than 200 ant species which exhibit aggressive and predatory characteristics during raids. During these foraging raids, large numbers of ants march over a certain area and forage for food.

Initially, army ants were thought to have evolved independently. In 2003, genetic analysis of several species indicated that they all evolved from a common ancestor which lived more than 100 million years ago when the continents of South America and Africa separated. Normally, a colony contains millions of individuals descended from a single queen.

Army ants have two unique characteristics: they are nomadic and exhibit group predation tendencies:

Nomadic and stationary characteristics

These ants have 2 phases of activity-a wandering phase and a stationary phase. These two phases are found in all army ant species.

The nomadic stage starts roughly 10 days after the queen lays her eggs. The phase lasts about 15 days to allow the larvae develop. During this phase, the ants move during the day as they capture small vertebrates and insects to feed their young. When night falls, the ants form a nest or bivouac which they modify daily according to their needs.

At the end of the nomadic phase, the larvae spin pupal cases and no longer needs to feed. This allows the colony to settle in the same nest for about 20 days. During this period, the ants forage only for 2/3 of the days.

The stationary period starts when the larvae pupate and lasts for about 3 weeks. During this phase, the queen is fed with food that was previously fed to the larvae. The abdomen of the queen distends significantly and she lays her eggs.

Towards the end of the stationary phase, the pupae emerge from the cocoons and the next batch of eggs hatch. This cycle ensures that there is always a new group of larvae and workers in the colony. Once the pupae emerge from their enclosions and the eggs hatch, the ants resume their nomadic life.

Group predation

A colony of army ants can consume about 500,000 prey animals daily. This can impact the diversity, behavior and population of their prey significantly. During the forage, trails formed by these ants can be over 20 meters in width and more than 100 meters in length. Colonies can have as many as 15 million workers and is capable of transporting more than 3,000 preys per hour during the forage. The ants stay on the path due to the use of pheromones produced by their fellow ants.

                                    Photo credit/ https://pixabay.com

Working as a team, the ants can kill larger animals such as poultry, lizards, small mammals and snakes. These ants are also known to climb trees, attack birds and carry off their young or eggs.

Habitat

Currently, there are more than 200 species of marabunta ants around the globe. These are found in southern United States and common in South America, Central America. The ants are also common in Africa and parts of Asia.

Legionary ants thrive in tropical regions and are commonly found in mountainous as well as volcanic areas. The ants can also be found in rainforests, lowland tropical forests, swamp areas and vast deserts. Though they commonly thrive in humid areas, the ants can be found in densely forested places and agricultural areas as they forage for food.

Army ants live in temporary nest and rarely make underground burrows unlike other ants. The temporary nests or bivouacs are places where the ants rest between their raiding expeditions. The nests can be out in the open or inside a hollow log.

A nest made of ants

Most of the time, the ants make the temporary lodging place by hanging from a tree limb. Thousands of worker ants link their mandibles and legs making an enclosed hammock for the queen. In some instances, the ants enclose the immature ants inside the hammock alongside the queen. The ants stay put in the temporary nest for weeks at a time until the queen comes out of her resting place. Once the queen emerges out of her resting place, the colony starts to migrate.

While some species of these ants move in a line, others move in a fan-shaped formation. The soldiers march at the side of the queen as a column ready to defend her in the face of any threat. During the march, some workers carry the immature ants while the others gather all the food they come across. As they march, the ants kill every insect, lizard or small mammal in their path.

Scientists have been studying these ants to find out why they migrate. In the past, scientists thought the ants migrated to find new sources of food; however, emerging evidence seems to suggest that the migration could be linked to the development of the immature ants and eggs in the colony. Scientists suspect that there is a link between the production of eggs by the queen and the colony’s migratory tendencies.

Anatomy

Legionary ants are normally brown in color; however, some are black. Their bodies measure 8mm-12 mm in length and have a lifespan of 3-13 months.

Just like other ant species, the bodies of army ants consist of a head, thorax and abdomen as well as 6 legs. The ant’s thorax is between the head and the abdomen and is linked to the abdomen by joints or nodes. Their abdomens are oval-shaped and feature a stinger.

The head has mouthparts, eyes and antennae. The mouth of army ants comprises of mandibles or 2 jaws which look like scissors. The antennae are used to touch, smell and communicate with fellow ants. Adult army ants do not have the ability to eat solid food but ingest liquids only.

Food habits

Legionary ants are carnivorous. Though these ants are perceived as voracious, most of them do not eat every kind of prey. Army ants prey on arthropods, earthworms, turtle eggs and the young of vertebrates. Some species known as colony robbers specialize in the offspring of wasps and ants. While small vertebrates get trapped during the forage and get killed, only a few species such as the African Dorylus eat such prey. In most circumstances, the undesirable prey is left behind for other scavengers that accompany the swarm to feed on.

While on the rampage, the ants climb trees, shrubs or go through houses. People have to move their livestock such as goats or poultry to save them from the marauding ants. Though the ants can be devastating to human settlements, they are also beneficial since they kill and carry away pests such as mice and roaches that are unable to get out of their way.

Interesting facts

Marabunta ants have a great digestive system that is capable of dissolving any living creature. Their colonies consist of a queen, soldiers and workers. Soldier ants have large jaws which they use to dig, kill and carry large prey.

The clamping ability of the army ant’s jaws is so powerful that natives in the rainforests used them to stitch up wounds. The natives would place an ant on the open wound and pinch the ant from behind to induce it to bite down on the wound. The ant’s body would be cut off to allow the head remain clamped down on the wound.