Acid-spraying insects with a soft side. Southern wood ants roam our woods in huge gangs and have a surprising approach to finding their favourite food.
Common names: southern wood ant, red wood ant, horse ant
Scientific name: Formica rufa
Family: Formicidae
Habitat: woodland
Diet: insects and invertebrates, aphid honeydew
Predators: birds, badgers may take eggs and larvae
Origin: native
The southern wood ant is the UK’s largest ant species with workers reaching 10mm in length and queens 12mm in length. It is a reddish-brown colour, with a black head and abdomen.
Worker: Length 4-6mm, reddish-brown- to yellow in colour with a dark patch on the head. Legs and body are hairy. They have large mandibles and spray formic acid as a defence.
Queen: up to 12 mm in length and brownish in colour with a lighter underbody.
Wood ants climb trees to reach aphids. Juniper, Scots pine, sycamore, birch and oak are all important host species for the small insects.
Southern wood ants are carnivorous and will actively hunt other insects and invertebrates such as caterpillars and spiders. However, their main source of food is honeydew, a sugary substance that is secreted by aphids (small insects that feed on plant sap).
To access this food source, wood ants have developed an unusual relationship with aphids. Ants will ‘tend’ to the smaller insects, stroking their abdomen with their antennae. This stimulates the secretion of honeydew. The aphids benefit from this relationship as the presence of the ants deters attacks from other predators.
Research has found that a single colony of wood ants may consume a quarter of a tonne of honeydew annually.
Southern wood ants live in large, complex social groups made up of three groups: queens, workers and males. Each group fulfils a specific role to ensure the survival of the colony. Males mate with queens, who then produce eggs. Workers, which are all female, are responsible for feeding the colony and maintaining the nest in which it lives.
In summer, huge numbers of winged males and queens will emerge from the nest, mating in mid-air. With their role fulfilled, the males will die not long after mating. The queens will disperse before shedding their wings and looking to establish new nests elsewhere.
When threatened by predators, wood ants can spray formic acid in a bid to defend themselves.
Southern wood ants are most numerous in the south of England and Wales, but can be found further north in smaller numbers. The species prefers to build its nests in open woodland glades that are well exposed to sunlight.
They are also fiercely territorial and will attack any ants from a different colony that enter their territory.
Credit: Alex Hyde / naturepl.com
Wood ant nests are large and conspicuous, so the species is relatively easy to find. Look out for dome-shaped mounds of grass, twigs, or conifer needles that have been collected by the ants. There may be up to 400,000 individuals in a nest and occasionally, several nests may be interconnected, forming a large colony. We have southern wood ants at our Fingle Woods.
Southern wood ants can send a jet of acid spray upwards from their abdomen. If you get too close you may smell the ‘chip-shop vinegar’ scent of formic acid, sprayed to ward off predators.
Southern wood ant is listed as Near Threatened on the global IUCN Red List of Threatened Species. It is relatively numerous in southern England and Wales, but has disappeared from much of the Midlands, East and North. Potential threats include loss and damage of woodland, overgrazing from deer and livestock and human disturbance.
