Wood Ants

Wood ants are large red-and-black ants that build huge dome-shaped nests out of pine needles, twigs and leaves on the forest floor. They belong to the genus Formica and live in Europe, Asia and North America. A single nest can hold hundreds of thousands of ants.

Scientific Classification & Quick Facts

Common name	Wood ants
Scientific name	Formica
Kingdom	Animalia
Phylum	Arthropoda
Class	Insecta
Order	Hymenoptera
Family	Formicidae
Type	Large, social mound-building ants
Diet	Insects, caterpillars, aphid honeydew
Habitat	Woodland mounds of needles and twigs
Native range	Europe, North America and Asia
Size	5 to 11 mm long
Lifespan	Queens 15+ years; workers about 1 year
Colours	Black and red

What Are Wood Ants?

The genus Formica contains more than 150 species. Different kinds are known as wood ants, mound ants, field ants and thatching ants, and people also call them horse ants. The name wood ant is usually used for the mound-building species that live in and around forests, such as the red wood ant, Formica rufa.

In Britain, the main wood ants are the southern wood ant (Formica rufa), the hairy wood ant (Formica lugubris) and the Scottish wood ant (Formica aquilonia). They are the biggest ants in the country.

What They Look Like

Wood ants have a reddish-orange body with a dark brown or black head and abdomen. Workers are usually about 5 to 9 mm long. Queens are larger, at around 10 to 12 mm. With practice, experts can tell the different species apart by details such as the hairs on the head and body.

Wood ants do not have a stinger. Instead, they can bite with their strong jaws and then spray formic acid from the tip of the abdomen into the wound. They also spray it to drive away enemies. If you put your hand near a busy nest, you may smell the sharp, vinegary scent of the acid.

The Wood Ant Nest

Wood ant nests are amazing structures. The ants pile up pine needles, twigs, bits of leaves and other plant material into a dome that can be a meter (3 feet) high or more. Many nests are built on old tree stumps. The mound is only part of the nest: underneath, tunnels and chambers reach deep into the soil.

Inside, the nest works a little like a busy town. There are chambers for the queens, nurseries for eggs, larvae and pupae, and passages connecting everything. The mound soaks up the sun’s heat, and the ants move the brood around to keep them at just the right temperature. In winter the ants retreat deep underground and become inactive, coming back to the surface in spring.

A large nest can contain hundreds of thousands of ants and several queens. Some species form supercolonies, where many connected nests share ants, adding up to millions of individuals. Nests can last for decades.

Life in the Colony

Almost all the ants you see are workers, and all workers are female. They do not normally mate, but they look after the nest, care for the queens’ young, gather food and defend the colony. Workers usually live for about a year. Queens can live for many years, possibly more than 15.

Males have just one job: to mate with new queens. Winged males and young queens leave the nest on mating flights in spring or early summer. The males die soon afterward.

Unusual Ways to Start a Colony

Many wood ant queens cannot start a nest on their own. Instead, a newly mated queen sneaks into the nest of another, smaller kind of Formica ant. The host queen is killed, and the host workers raise the invader’s eggs as if they were their own. As the host workers die off, the nest becomes a wood ant nest. Scientists call this temporary social parasitism. A new queen may also be adopted back into an existing wood ant nest.

A related ant, the blood-red ant (Formica sanguinea), goes even further. Its workers raid other ant nests, carry off the pupae and raise them as extra workers. For some ants this behavior is essential for survival, while others can manage without it.

Hunting and Foraging

Wood Ants – Photo by: Paul Dickson

Photo by: Paul Dickson

On warm days, long lines of workers stream out of the nest along well-worn trails, leaving scent marks so they and their nestmates can find the way home and to good food sources. Wood ants do not see very well. They mainly find prey by smell and by sensing vibrations.

Wood ants are fierce predators. They hunt caterpillars, beetles, flies, spiders and other small creatures, and they also collect dead insects. When prey is too big for one ant, others join in to overpower it with bites and formic acid. A big colony can catch many thousands of insects a day, including pests that damage trees.

Many other small animals live inside wood ant nests, including beetles, mites and other insects. Some are scavengers that eat waste, and the ants largely ignore them.

Farming Aphids

The most important food for wood ants is not prey at all but honeydew, a sugary liquid made by aphids and other sap-sucking insects. Workers climb trees and stroke the aphids with their antennae, which makes the aphids release droplets of honeydew. In return, the ants protect the aphids from predators, a bit like a farmer looking after a herd of dairy cows. Now and then the ants also eat some of the aphids.

Where Wood Ants Live

Wood ants are found across Europe, northern Asia and North America. Most mound-building wood ants live in coniferous and mixed woodlands, where there are plenty of needles and twigs for nest building. They usually build nests in sunny spots such as clearings, glades and woodland edges, because they need the sun’s warmth. A few species, such as the hairy wood ant, cope better with shade.

Other Formica species prefer open grasslands, heaths, scrub, bogs and coastal areas. In North America, many of these ants depend on open habitats that were once kept clear by natural fires. Changes in land use and fire control have reduced some of these habitats.

Why Wood Ants Matter

Wood ants are important for forests. They eat huge numbers of insects, spread seeds, help recycle nutrients and are food for birds such as woodpeckers. In some places wood ants are declining because of habitat loss, and the red wood ant is listed as Near Threatened. If you find a nest, enjoy watching from a short distance, and never poke or disturb the mound.

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