The wonder of Winter Moths

Drive on wooded lanes and near hedgerows on calm, mild nights in winter and you can’t miss the fluttering forms in the headlights. These are male Winter Moths (Operophtera brumata) and they’re looking for mates. The females they seek are very different animals; almost wingless and unable to fly. They crawl up a tree trunk to a suitably lofty height where they emit the pheromones that will attract a male. Look for them in woods with a torch any time from October until January.

Female moth has greatly reduced wings and is unable to fly.

Female sits, normally on a tree trunk, and emits pheromones to attract a mate.

Male moth flies in search of the female. Once located they mate on the food plant where eggs are then laid.

Male and female Winter Moth. Photo: Biosphoto (Alamy Stock Photo)

This moth, although rather dowdy, has extraordinary biology. Not only has the female dispensed with flying, but they are also able to tolerate winter temperatures by producing compounds that stop them from freezing. The eggs, once laid on twigs or in fissures on bark, remain dormant until the spring, awaiting the flush of new plant growth. Oak, birches, Hawthorn and heathers are favoured, but they will use a wide variety of food plants. When they hatch, the caterpillars set to work devouring the soft, new leaves. In turn, the huge numbers of Winter Moth caterpillars are an important food source for many bird species.

Should they exhaust a particular food-plant, the caterpillars can even ‘balloon’ to pastures new, spooling out a long line of silk that carries them aloft via electrostatic repulsion – much the same as spiders. By June, fully grown caterpillars tumble to the ground to pupate in the soil – awaiting the shorter days and falling temperatures that will trigger adult emergence.