Country diary: England's only narrow-headed ants are toughing out winter

South Devon: Outside this field the nearest colony of these heathland ants is in the Scottish Highlands

A soggy mound amid the grass stopped me in my tracks. I had spent the best part of an hour searching the heathland reserve, eyes to the ground, before I chanced across it close to a clump of gorse. It was nothing much to look at, admittedly. After a winter of heavy downpours the dome-shaped structure covered with tiny snippets of vegetation had slumped so that it resembled a spadeful of old lawn clippings. Yet beneath the bedraggled thatch was buried treasure: an exceptionally rare colony of narrow-headed ants (Formica exsecta) toughing out the colder months hidden from view.

Shaped like tiny lopsided dumbbells, these territorial ants, named for the distinctive notch in the back of their head, play an important role in maintaining heathland through their foraging behaviour. Colonies can contain several queens along with about 1,000 workers, each armed with strong mandibles and capable of engaging in chemical warfare by firing jets of formic acid from their rear to deter predators.