Silky field ant
Formica fusca
Where it comes from
- Range
- Europe and northern Asia, in open woodland and clearings
- Size
- Workers 4–7 mm, queen 8–10 mm
- Queens
- Usually one queen
Keeping them
- Diet
- Sugar water and insects
- Founding
- Fully claustral — the queen needs no food until her first workers
- Brood development
- Egg to worker in roughly 5–7 weeks at 25 °C
- Nest
- Ytong or plaster with a damp corner and a large outworld to run in
- Wintering
- 5–10 °C, and they want the full length of it
Fast, skittish foragers that scatter when the nest is opened. They want a long, genuinely cold winter.
Starting a colony
Formica fusca queens fly in summer. After the flight they are easy to spot walking alone on paths and forest edges: black, with a faint silky sheen, and 8–10 mm long. A queen without wings has mated.
House her in a test tube: water at the back behind a plug of cotton wool, the queen in the dry front half, and a loose plug at the opening. Cover it, keep it at 22–26 °C and leave it alone. She is fully claustral and lives on her own reserves until her first workers arrive. Formica is quick: at 25 °C, egg to worker takes roughly 5–7 weeks. The larvae spin cocoons before they pupate, so the first sign of progress is often a small pile of pale cocoons next to the queen.
The first workers are small and nervous. Formica fusca relies on running rather than fighting, and it shows from the start: lift the cover and they scatter, often carrying brood with them. Keep the tube covered and look as little as you can.
Feeding
In the wild this species collects honeydew from aphids and hunts and scavenges small insects. Give sugar water or diluted honey, and insects whenever there is brood: fruit flies, crickets, cut mealworms. Unlike Lasius, Formica fusca hunts live prey readily, so a small live insect dropped into the outworld is often caught and carried in. A colony with a lot of brood eats more protein than you might expect. Remove dead remains after a day.
The nest
A young colony stays in its test tube until the tube gets crowded. After that, a Ytong or plaster nest with one damp corner suits it, with a larger outworld than a Lasius colony would need. These are fast runners with good eyes, and they use the space.
Formica workers climb smooth walls, so the barrier along the top of the outworld — PTFE (Fluon) or a thin film of paraffin oil — is not optional, and neither is a lid. Plan how you will open the setup before you do it: a nervous colony that bolts is gone in seconds. Most colonies stay at a few thousand workers at most, and growth in the first year is quick by the standards of European ants.
Hibernation
Formica fusca needs a winter rest from October to March at 5–10 °C, in a cellar, an unheated room or a fridge, and it does badly on a short or mild one. In autumn, lower the temperature over a couple of weeks and stop offering insects. Check the water every few weeks, because a test tube that dries out over the winter kills the colony, and in spring warm them up just as gradually.
Common mistakes
- Opening the nest often. Every disturbance sends the colony running, brood and all.
- Cutting the winter short.
- An outworld without a barrier or a lid.
- Moving a small colony into a big nest too early.
- Too little protein while there is a lot of brood.
Questions keepers ask
Why do they run away? Because that is how the species survives. Formica fusca is a host for slave-making ants such as Formica sanguinea and Polyergus, which raid its nests for brood, and for the queens of the red wood ants, which take over a fusca nest to start their own colony. A species that is raided and invaded that often has evolved to flee rather than fight.
How long until the first workers? About 5–7 weeks at 25 °C, which is quick for a European species.
Does it sting? No. Like every Formica it can bite and spray formic acid from the tip of the gaster, but it is harmless to people.
Is it a good first species? Yes, as long as the setup is escape-proof. If you want a calmer colony to start with, Lasius niger is the classic choice. If you want a bigger, faster ant to watch hunting, Formica fusca is a good one.
Check it yourself
General guidance from the usual beginner references — treat it as a starting point, not as a rule your colony has agreed to.
Start a colony with this species
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