Wood ants

The World of the Wood Ant

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We’ve long known that ants are intelligent, social and complex organisms. And if you’ve ever been lucky enough to chance upon a wood ant nest, you will have seen some of these clever, sophisticated insects in action. You will probably also have been amazed by the nest’s huge size, dwarfing the individual inhabitants. So, what makes a wood ant tick and what goes on inside those mighty woodland structures?

What Are Wood Ants?

The UK has three species of true, or red, wood ant. The largest of these is the southern wood ant, Formica rufa. As its name suggests, this lives in more southerly parts of the UK, although there are outposts as far north as Cumbria. The hairy wood ant, Formica lugubris, is found in suitable habitat in North Wales, upland England and the Scottish Highlands. The Scottish wood ant, Formica aquilonia, is confined to Scotland and parts of Northern Ireland. The European wood ant, Formica pratensis, was once also an inhabitant of mainland Britain. It is now only found on Jersey and Guernsey. The Formica part of the genus’ scientific name refers to the formic acid these hugely territorial insects are able to spray at attackers.

Wood ant nest
Wood ants build huge domed nests

Apart from some geographical distinction in the case of the southern wood ant, all three mainland wood ants are difficult to tell apart without a microscope. Workers range in size from 4 to 9 mm in length depending on how well they fed as grubs. Queens are up to 12 mm long. All have reddish thoraxes (the central section of every insect’s three-part body). The heads and abdomens are usually blackish brown. As such, most of the information here refers to all three. Unsurprisingly, one thing that distinguishes this group from similar species is their liking for woodlands (usually coniferous). They will sometimes build their nests on heathland, however. The dome-shaped nests are also an identification aide. Basically, those species that also build overground structures don’t build anything as large as wood ants do. The largest nests can measure up to two metres in height, with as much again hidden, iceberg-like, below the ground.

Home Sweet Home

Inside, the nests contain a network of tunnels along with chambers for the queen or queens, brood rearing and storing food. Pine needles, twigs, heather and grass thatch the exterior. Thatch components are arranged in such a way as to get the maximum warmth from the sun and raise the nest’s temperature to the optimum 28 – 30˚C range. Nests are also usually south facing and built in woodland glades or on the edges of rides for the same reason. This heat is vital to help the colony’s grubs grow. The ants can also regulate the nest’s internal temperature themselves. As well as closing and opening tunnels to increase or decrease ventilation, they also move vegetation around and sunbathe on the surface of the nest before going back inside to transfer that heat to the inner chambers. In addition, they sometimes move grubs to warmer chambers or even out to the surface to warm up. Finally, the nest’s thatch is also largely waterproof and able to deflect rain.

Wood ant nest
Tree trunks sometimes offer support for the nests

Nests can house up to 400,000 individuals, with some forming part of larger colonies of interlinked nests. The majority of these ants are female workers, with their gender determined by the fact they came from one of the queen’s fertilised eggs. Infertile eggs produce males whose sole purpose is to mate with a queen. Workers, meanwhile, have an array of roles. As well as building, maintaining and defending the nest, they forage and feed the queen’s larval offspring. Grubs get mostly protein-rich invertebrates with those destined to become queens getting more food. Incredibly, workers get much of their own food and that of the queen by ‘milking’ aphids for honeydew. Aphids excrete excess sugars from their tree sap food. The ants seek them out, stimulate them to excrete the substance by stroking their abdomens, and carry the honeydew back to the nest in special crops. In return, the aphids get protection from predators such as various ladybird species.

The Wood Ant’s Year

Each autumn, wood ant queens, along with a small number of workers, hibernate deep within the underground chambers of each nest. The overwintering workers emerge the following spring, usually around March, but later if temperature and sunshine levels aren’t high enough. Once emerged, they swarm over the nest surface in the sun, absorbing its heat. The queen, meanwhile, begins egg-laying. Workers soon begin foraging for insect prey for the first grubs of the year, destined to become either queens or males.

Once temperatures are warm enough, wood ant nests are full of activity

Like all insects, the grubs metamorphosise within a cocoon in order to become adults. The winged queens and males emerge from these cocoons over a few weeks in the summer, again depending on temperatures. Males disperse more widely in order to mate with queens from unrelated nests, thus preventing interbreeding. Mating itself often takes place in airborne nuptial flights, with the males dying shortly afterwards. Once mated, the queen loses or chews off her wings. With the new queens and males gone, workers are free to spend the rest of the summer raising new female workers within the nest.

Flying wood ant
Only queens and males have wings

Only a tiny proportion of mated queens survive to establish their own colony. Most are predated by birds or other invertebrates, including other ants. Some survivors form a new colony by taking over another ant species’ nest. Once inside the nest, the invading queen sets about gradually replacing the existing worker population with her own offspring. Other wood ant queens will return to the nest she hatched in, with the nest then housing multiple queens. Some returning queens instead set up an adjacent offshoot nest in a process called budding. Although males live for just a few weeks and workers for approximately 2 months, queens can live for up to 20 years. And as long as it has a queen, wood ant nests can survive for decades, with daughter queens often ensuring its survival once an existing queen dies.

Woodland Wonders

We have known for some time that ants have large brains in proportion to their body size. Like bees, they are able to learn from their experiences and have exceptional navigational abilities and good memories. Some ant species even use tools, long held as an indicator of a species’ intelligence. Exceptionally strong, many ants are able to lift objects over 100 times their own weight. Like other ants, wood ants are also vital components of healthy ecosystems. By predating other invertebrates, they keep their prey populations in check. In this way they protect trees from over-infestation of caterpillars. They also help plants by dispersing seeds.

Wood ants
All three true wood ant species have orange thoraxes and blackish brown abdomens

In addition, they are themselves prey for other animals, including green woodpeckers and badgers. Some birds also use them, along with other ant species, for a process called anting, thought by some to help them stay free of bacteria and parasites. Wood ant nests are important for a number of other invertebrates, too. The rare and much smaller shining guest ant only lives in the thatch of wood ant nests, for example. And it is thought that the bright green rose chafer beetle lays its eggs in wood ant nests so that its larvae can then feed on any debris within. The ants tolerate the larvae as they help keep their nest clean and tidy.

A typically busy wood ant nest in the sunshine

Marching Onwards?

Despite their importance for woodland habitats, all three of our true wood ant species are classed as Near Threatened by the International Union for Conservation of Nature, or IUCN. Habitat fragmentation, changing land uses and insect prey declines are all threats. Many of their strongholds are in working forestry sites, so getting the balance right between necessary tree-planting and leaving open areas that sunlight can reach is crucial.

Wood ant nest
A wood ant nest being overgrown with bilberry

Increased housebuilding, even within national parks such as the Cairngorms, is also removing vital habitat and increasing disturbance from recreational activities. Nests only produce queens once they are well-established, a process taking about five years on average. As such, disturbance can have a huge impact on the establishment of new colonies and the maintenance of stable populations. We need to ensure that we don’t further jeopardise the existence of these fascinating and important insects.

Further Reading

For much more information on our three species of true wood ant, along with some of their fellow wood-dwelling cousins, see the UK Wood Ants website. Set up to help put conservation measures into practice and policy, there is a wealth of information and resources on every aspect of their lives.

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