The Formica rufa Group: Which Red Wood Ant Species Is It?

Nov 2

3 min read

Updated: 1 day ago

"Red wood ant" is often used as the name of one species, Formica rufa. In reality, there is a whole group of species that look very much alike and live in a similar way: the Formica rufa group. Even experts sometimes need a microscope to tell them apart. Here are the species, and the clues that help you recognise them.

What do they have in common?

All species in the group have a reddish head and thorax and a dark gaster. Workers grow up to about 9 to 10 mm. They build mounds of needles, twigs and other plant material, and their young queens cannot start a colony alone: they need the help of workers of another Formica species, or they are taken back into an existing nest. Read more in our red wood ant facts.

The species of the lowlands

Two red wood ant workers on pine needles — Two red wood ant workers. Telling the species apart often takes a magnifying glass.

In the Netherlands, four species of the group occur:

Formica rufa: upright hairs on the front of the thorax. Common on sandy soils. Young queens often fly off after mating to start new nests, so nests are often on their own.
Formica polyctena: few or no upright hairs, which makes it hard to tell apart from Formica rufa. Young queens return to their own nest, so nests have many queens, grow very large and often lie in groups.
Formica pratensis: a black spot on the top of the thorax. Its mound is flatter and lies in a wide crater with raised edges. Usually one queen.
Formica truncorum: completely red and very hairy. The rarest of the four in the Netherlands, known only from the area around Ommen. Usually one queen.

The species of the mountains and the north

Formica lugubris: very hairy, with a fringe of hairs reaching down to the eyes. Lives mainly in conifer forests in the mountains and uplands, such as the Alps, the Jura and the Pyrenees.
Formica paralugubris: almost identical to Formica lugubris. Lives in the Alps and the Jura and forms huge supercolonies with hundreds to thousands of nests.
Formica aquilonia: a species of cool conifer forests in northern Europe and the mountains.

Outside Europe there are more members of the group, such as Formica yessensis in Japan, famous for the largest wood ant supercolony ever found. Read more in wood ant supercolonies.

Why are they so hard to tell apart?

Close-up of a red wood ant worker seen from the front — A red wood ant worker up close.

The differences are small and mostly come down to hairs: how many there are, where they are and how long they are. On top of that, hairiness varies between individual ants, and some species, such as Formica rufa and Formica polyctena, can hybridise. That is why even experienced myrmecologists often need a microscope and several workers from the same nest.

Tips for recognising them

Look at the hairs on the thorax and the back of the head with a magnifying glass.
Check the nest: is it on its own, or part of a group of nests close together?
Look for a black spot on the back of the thorax: that points to Formica pratensis.
Is the ant completely red and very hairy? Then it may be Formica truncorum.
Think about where you are: lowland forest, mountains or the far north.

Whatever species it is: leave the mound alone. Read why in how a red wood ant mound works and why red wood ants are good for the forest. Want to keep red wood ants yourself? Read our Formica rufa care guide.