Country diary: Winter moths have the best and wildest party of all

The lights are on late – and that means moths. Tonight, one is just resting on our kitchen window, looking somewhat forlorn, on the outside looking in, incidental and uninvited. These visitors this time of year are usually winter moths (Operophtera brumata).

Tonight, when lights will be on in many places till the small hours, it would be easy to think that the moths are the ones missing the party, dressed in the dullest of grey-brown and having little to do but flutter about on gossamer-thin wings. But that would be quite wrong. Theirs is the best and wildest party of all. The air of winter dusk reeks of pheromones. The females are flightless, and on mild nights they climb trees and send out chemical messages that charge the atmosphere with possibility. It’s a lust-fest out there. The males hasten to the treetops to copulate. Sometimes in their zeal they fly off with their mate still attached. The flightless take a flight – what a way to start the year!

Assuming they return to the trees, the females lay their eggs in the bark and in spring the caterpillars hatch, with the intention of meeting the leaf-burst. In oak woods there is an arms race between tree and caterpillar. If the caterpillars hatch at just the right time, when the leaves are fresh and delicious, they might completely defoliate and damage the tree; if the oak brings leaves late, the larvae might all starve. But the caterpillars have an emergency plan for the latter; they let themselves down on silk threads and hope the breeze wafts them to better fare.

There is another player in this drama, the blue tit. Blue tits in woods may rely on an abundance of winter moth caterpillars to feed their brood. For them, a good caterpillar crop is essential, so they need the larvae to prosper.

A blue tit might meet a winter moth tomorrow. Blue tits are winter vegetarians; their guts are adapted so. They won’t eat the moth and won’t have any idea that this flying neighbour is the key to their breeding success in a few months’ time.

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