In the days when I used to run a moth trap regularly, I can’t recall a night when I didn’t catch something. Even in the dead of winter, a wide selection of moths is on the wing on all but the chilliest of evenings. But don’t take my word for it: despite lockdown you can confirm this for yourself, and without the need to run a moth trap. If you have a reasonably bright outside light, leave it on overnight and you will find moths in the vicinity the following morning, sitting on the wall and on nearby surfaces. That’s assuming the local Robins don’t discover this food supply.
You may wonder why on earth a moth would evolve to be on the wing in the middle of winter. Who knows for sure, but a couple of suggestions spring to mind. Firstly, it might be a case of getting ahead of the game: by mating and laying eggs before leaves are even in the fully-formed bud stage, larval emergence can be timed to coincide with the freshest and juiciest young foliage as it appears. Another possible advantage is that there are fewer mammalian and avian predators around at that time of year. However, if this is the strategy then it’s not entirely successful: on mild nights the occasional pipistrelle will wake from slumber to snack on adult moths and birds such as Goldcrests somehow find the moths’ eggs in the daytime.
Whatever the reason, plenty of moth species do just appear in winter. Their eggs hatch in spring and the resulting caterpillars are so important as a food source that birds such as Blue Tits and Great Tits align their nesting so their hungry chicks hatch when the larval biomass is at its peak.
Hibernation – Interestingly, another group of moths emerges in the autumn and hibernates through the worst of the cold weather, reappearing again in spring. However, during mild winter spells they sometimes emerge and appear at lights. Hibernation sites include garden sheds and cosy tree holes.