Formica rufa (Red Wood Ant)

With their large mounds the red wood ants can claim gigantic territories. This ant species is famous for their aggressive behavior and that they happily shoot formic acid at its enemies. The population of Formica rufa colonies can reach well beyond 100.000 workers.

ant species formica rufa

Appearance

Worker: Length 4,5-9 mm. The workers are quite hairy. Although they mostly don’t have more than two hairs on the back of the head. The head and forehead is dark. The cheeks have a red and brown shade which also covers the mouth area and mandibles. Red and brownish middle segment with a dark spot on the upper front part of the segment. The abdomen is a flat dark brown or black and brown shade. The legs as well as the antennas have the same color as the middle body or a slightly darker shade.

Queen: Length 9,5-11,5 mm. Do not have hairs on the front of the abdomen, which is something otherwise common in other species of wood ants. The first part of the abdomen is more shiny than in other species. Color wise the queens have quite similar covering as the worker. What sets them apart is the shine of the abdomen which is greater in the queens. The dark spot on the middle segment is there, but it’s greatly enlarged. It almost looks like a black shield completely covering the upper part of the middle body.

Male: Length 9-11 mm. No hairs on the cheeks and only a few on the outside of the thighs. Very difficult or impossible to differ from the males of Formica polyctena. The abdomen of the males is, just as the queens, more shiny than that of the workers. At the same time their bodies are almost completely brown and black with slightly brighter legs. (1)

Formica Rufa worker red wood ant with black

 A Formica Rufa worker sporting its classic red and black color. Photo: Richard Bartz, Munich Makro Freak CC BY-SA 2.5

Formica Rufa ant nest

A very classic Formica Rufa nest situated in the middle parts of Sweden. Photo © Antkeepers

Distribution

Formica Rufa is found throughout Europe with the exception of the most southern parts. The distribution of the red wood ant is wide. From the middle parts of the Northern European area all the way east to Mongolia.

Habitat and Nest

Formica rufa is the center species of the mound building family of wood ants (the family is actually called Formica rufas and consist of a total of five species). They build enormous ant hills in coniferous as well as deciduous forests. This means that they settle by both the pine needles as well as the leave bearing trees. But they seem to like the pines more than anything else. Their mounds are often the shape of domes but they can also be more of a flat build when the ants settle out in the open. Some species of the Formica family sometimes even build inverted domes, with a dip in the middle. (2) This is probably a way of taking better advantage of weather and surroundings. Read more about ant hills here.

Behaviour

The red wood ant seldom settle their colonies near each other. The ant hills are sparsely placed and often far away from other nests. Some sources claim than the Formica rufas have one or a few queens whilst others claim they can have hundreds of them. Most likely is that the species in general have a more monogyne setup with most having only one queen. (3) The workers are easily spotted outside of the nest since they tend to quickly move around their territory. Their ant roads can reach up to a hundred meters from the nest and are used to gather food and supplies. Formica rufa tend to keep aphids as livestock. They protect them and their host plant in exchange for the sweet honeydew that they emit when touched. There are reports of a Formica colony carrying as much as 500 kg of honeydew back to the colony in a year. (4)

Formic Acid

Formica rufa can shoot formic acid from their abdomens. It is produced by poison glands in their behinds. This is something the ants successfully use to defend themselves and the colony. If a nest of red wood ants are disturbed the air will soon be filled with a pungent smell. The acid is colorless, liquid and corrosive and is called acidum formicum in latin (from Formica, meaning ant in latin). Formic acid is one of the simplest organic acids but still relatively strong. In larger amounts it should be dealt with with caution. (5) More on formic acid here: Wikipedia | Formic acid

Formica rufa worker tending to aphids for honeydew

A Formica rufa worker guards and “milks” aphids for their sweet honeydew. Photo: Richard Bartz, Munich Makro Freak CC BY-SA 2.5

Nuptial Flights

The nuptial flights of Formica rufa happens from the middle of May to the beginning of July. The flying ants most often go outside early in the day or in the beginning of the afternoon. The mating is handled on top of the ant hills or in classic flying manner. (6) New colonies are not established by a single brood bearing queen (claustral), but instead they conduct nest founding through parasitism. The newly mated queens aim to take over an already functioning nest of another ant species (in most European cases the species of Formica fusca or Formica lemani). What sets the red wood ant queen apart from other parasitic ant queens is that she does not employ advanced strategies such as playing dead or using smell to confuse the workers. Instead she simply make a run for it, head first straight into the colony. Like a sprinter she bets her life on being able to get inside and take over as queen before the workers kill her. In most cases she does not survive. But the success of the Formica rufas throughout Europe suggests that many queens are in fact not running in vain. (7)

Lifespan

These numbers are unfortunately not confirmed by researchers. The lifespan of Formica rufa is reported throughout the internet, but should be taken more as an estimation from enthusiasts: Lifespan of the queens: 10 years. Lifespan of the workers: 1-3 years.

Number of Queens

There seems to be a difference in number of queens depending on the geographic location of the species. In some parts of Europe and regionally in Sweden the ant species looks completely monogyne. In other parts of the world there are reports of multiple queens. This is all very confusing and when comparing references across the internet it does not get any clearer. Fortunately the ant bible “The Ants” clearly describes the state of queens in the Formica rufa species as monogyne (in most cases). Several other species of the Formica rufa family are polygyne.

Castes

The Formica rufa family has an interesting caste system that’s been observed in Formica polyctena. The workers are divided into three groups. 1: The Arboreal ants who gathers honeydew from their livestock (aphids) up in the plants of their territory. They can sometimes hunt for prey but primarily tend to gather honeydew. 2: Ground searching workers hunting for prey and food on ground level. 3: Ground searching workers foraging for building material for the ant hill. The workers can freely move in-between these groups but tend to, by observation, stick to one role for at least two weeks before switching. Research shows that the workers have different work ethics. Some are very varied and helpful in a great variety of tasks, while others are more focused and passionate about their current group belonging. (8) Read more about castes here: Ants | Caste Systems in Ant Societies

From Egg to Ant

5-6 weeks. (9) What can be said about the brood process of Formica rufa is that their larvae spin yellowish cocoons when they pupate. Often mistaken for ant eggs. The real ant eggs are of course much smaller, whiter and more transparent.

Captivity

It’s not easy getting your hands on a colony of Formica rufas. Most ant shops do not sell the species and the reason for this is a bit unclear. It’s also a species that’s not super easy to go out and capture since they have enormous nests. What makes it even more difficult is the way they found colonies. One simply can not go out and catch a new queen as easily as with many other ant species.

Something that is important to bear in mind if you keep Formica rufa is that they need a big formicarium. Otherwise, when the colony grows and they get stressed they might kill themselves by filling the air in the formicarium with formic acid. And that’s no fun!

Formica Rufa nest in wood forest

A classic Formica rufa nest in a secluded but sunny location. The colony is protected from hard weather by the surrounding vegetation and trees. At the same time they get the warmth of the sun for most of the day. The perfect spot! Photo © Antkeepers

A short documentary on the Formica family:

A video about wood ants from around the globe:

References:

1. Per Douwes, Johan Abenius, Björn Cederberg, Urban Wahlstedt (2012) Nationalnyckeln ”Steklar: Myror-getingar. Hymenoptera: Formicidae-Vespidae” p. 162, 164, 183-184

2. Per Douwes, Johan Abenius, Björn Cederberg, Urban Wahlstedt (2012) Nationalnyckeln ”Steklar: Myror-getingar. Hymenoptera: Formicidae-Vespidae” p. 164

3. Comparison between Nationalnyckeln p. 184, AntWiki | Formica rufa and The Ants p. 450

4. Bert Holldobler & Edward O. Wilson (1990) ”The Ants” p. 524

5. Formic acid – Wikipedia

6. Per Douwes, Johan Abenius, Björn Cederberg, Urban Wahlstedt (2012) Nationalnyckeln ”Steklar: Myror-getingar. Hymenoptera: Formicidae-Vespidae” p. 183

7. Bert Holldobler & Edward O. Wilson (1990) ”The Ants” p. 450

8. Bert Holldobler & Edward O. Wilson (1990) ”The Ants” p. 341

9. Bert Holldobler & Edward O. Wilson (1990) ”The Ants” p. 174

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