Strange Ants - Herders, Farmers, Dracula Ants and Zombies

Ants have an intricate colony organization and amazing lifestyles. Some ants have developed especially interesting ways of life. There are species that herd caterpillars, moving them around according to the time of day and “milking” the caterpillars by stimulating them to release a sweet secretion, which the ants eat. Other ants tend aphid colonies, stimulating the aphids to release honeydew and protecting the aphid eggs. The queen of one type of ant feeds on the blood of her larvae, reminding scientists of the Dracula legend.

Some ants have a close relationship with fungi. Certain species chew pieces off leaves and place them in underground nests. Here the leaves serve as food for a bountiful fungi colony, which the ants eat. In a strange twist of the ant-fungus relationship, some ants are invaded by a fungus that enters their brain and controls their behavior. The ants become zombies. The fungus forces the ants to behave in a way that benefits the release of fungal spores.

About 10,000 species of ants have been identified, but scientists think that around twice as many species actually exist. According to the AntWeb website run by the California Academy of Sciences, more than one thousand trillion individual ants are thought to exist on Earth. Who knows what strange ant behaviors are still waiting to be discovered!

Ants live on all continents except Antarctica, with the greatest variety of ants found in tropical regions. All known ant species live in colonies. An ant nest is often a complex underground home with many tunnels and chambers. There may be a raised ant hill above the nest, which also has tunnels. Ant colonies have a queen who lays eggs, males to fertilize the queen, and workers (non-breeding females) to collect food, maintain and protect the nest, rear the young and take care of the queen. The males have one job – to fertilize the queen ant – and don’t live for very long.

Ants and Caterpillars

The caterpillars of many butterflies in the Lycaenid family have a special relationship with ants. Lycaenid butterflies are sometimes known as blues, coppers or hairstreaks. The relationship between the caterpillars and ants takes several forms, but it’s often beneficial for each insect. The ants crawl over the caterpillars and trigger them to release a sugary solution by touching glands on the caterpillars’ bodies with their antennae.The ants then drink the solution. The ants are often said to be “milking” the caterpillars. Some species of ants even build shelters for their caterpillars. At night the ants protect the caterpillars in the shelters. At the start of the day the ants herd the caterpillars up a tree so that the caterpillars can feed on leaves. The ants guard their herd during the day.

Ants and Aphids

Aphids are small insects found around the world, but are most common in temperate areas, where they are major plant pests. Aphids have a wide range of colors. They may be colorless, pink, red, yellow, green, brown or black. The green forms are sometimes known as greenflies. Aphids have mouth parts than pierce plant veins and suck up the sugary sap that is being transported in the phloem vessels of the veins. Once they have digested the sap, the aphids release a sweet liquid called honeydew from the ends of their abdomens. Some ant species drink this liquid. An ant colony "farms" its own aphids, carrying them around to new plants when necessary, and stimulating the aphids to release a drop of honeydew by tapping an aphid with either an antenna or a foreleg. The ants attack predators that threaten the aphids. Some ant species collect the aphid eggs and store them in the ant nest over winter, taking the eggs back to the feeding plants in the spring.

Dracula ants are believed to be related to the first ants, which evolved from wasps. Dracula ants live underground and the workers are blind. The queen and workers of a Dracula ant colony bite holes in the ant larvae and then feed on their blood. Although this process sounds dramatic, the wounds and blood loss don't kill the larvae. Researchers refer to this feeding method as "non-destructive cannibalism". An ant’s blood is called hemolymph and is colorless.

Leafcutter ants are found in the tropics and in the southern United States. They cut off pieces of leaves or petals with their sharp jaws and then carry the plant pieces to their nest. Leafcutter ants are sometimes known as “parasol” ants, since they travel holding their leaf or petal pieces above their heads. They may collect material from plants as far as 250 meters away from their nest, and find their way back home by following a trail of chemical pheromones which they deposited as they traveled away from the nest.

The leafcutter ant colony contains several types of ants of different sizes, each with specialized functions. The largest ant is the queen. Next in size are the soldiers, who protect the nest. Smaller worker ants collect the plant pieces. In the nest, the leaf carriers pass the leaves to even smaller ants, who chew the leaves and turn it into a mulch. The mulch supports the growth of a specific type of fungus, which the ants – especially the larvae – eat. The smallest ants of all, called minima ants, take care of the fungal garden.

The ants tend their fungus crop carefully, cleaning it of debris and even destroying invading fungi of a different kind. Bacteria live on the surface of the ants. These bacteria produce antibiotics, which rub off the ants’ bodies and on to the fungus crop, killing the invading fungi.

Spores of a fungus named Cordyceps (or Ophiocordyceps), enter certain species of tropical carpenter ants as they walk over the forest floor. The spores then geminate inside the ants, producing the thread-like mycelium which makes up the body of the fungus. The mycelium spreads through the body of an infected ant, eventually reaching the brain and releasing chemicals which affect the ant's behavior.

Under the influence of the fungus, the ant moves to the underside of a leaf which is located in a specific height range above the ground. The ant then bites down hard on a leaf vein, attaching itself to the leaf. The temperature and humidity in this region are ideal for fungal spore survival. Interestingly, the fungus mycelium doesn't affect the muscle that control the ant's jaws, so the zombie ant is able to cling to the leaf. The ant dies but maintains its grip on the leaf. The myeclium sprouts from the ant's head and releases spores, which infect more carpenter ants when they come down from the forest canopy to the ground. Researchers have found that many fungus-controlled ants attach themselves to leaves at the same time, forming an ant graveyard. The scientists are very interested in learning how a fungus can control the behavior of an insect in such a specific way.