THE FASCINATING WINTER MOTH

This month and right through the winter you may well come upon a little brown moth with a wingspan of about 30mm resting under the light of your porch or on the window of a well-lit room. If it looks like the one below, it is Operophtera brumata, whose vernacular name is the winter moth. Some know it as the Evesham moth because it was such a pest in the orchards of that area of Worcestershire at one time, one of the worst outbreaks being 1868/69. Kent’s orchards were also a honeypot for this moth’s voracious larvae.  It has a very similar relative that is a little larger and paler called the northern winter moth O. fagata. Both are common in Britain. 

This little moth is a real toughie and manages well in sub-zero temperatures, although you are more likely to see it on milder nights. It has a fascinating life history. Males are not powerful fliers but, as you can see, have a full set of wings. The females, though (inset lower left of the illustration) are almost apterous, having just vestigial apologies for wings. They don’t need them because they crawl from their pupae when mature and up the stems and trunks of trees and shrubs. They then emit a powerful sex pheromone that wafts on the breeze and attracts the males that have emerged a few days before.  After fertilization, the females deposit their ova, as many as 100 per female, on budded shoots of the host shrub or tree.  Winter moths are univoltine (have a single brood in a year) and euryphagous which is to say their larvae eat many plant species. Fruit trees are a favourite, hence the moth’s bad reputation, but the larvae also feed on oak, birch, buckthorn, sallow/willow, hawthorn, hazel and many others. 

The ova hatch in the spring after overwintering, the young larvae boring into the host plant’s swelling buds. They consume the young bud tissue for a while, moving from one bud to another and then eat young leaves as these emerge. The larvae are of the typical “looper caterpillar” type (inset lower right of the illustration) of the Geometridae, the family to which this species belongs, mid to pale green with paler longitudinal stripes. 

The larvae feed and spin shelters amongst the foliage of the host species until they are about 3cm long when extended, attacking leaves and early fruit. They are usually mature by the first part of June when they descend to the ground to pupate in the soil where they create a small chamber a few centimetres below the surface in which a silken cocoon is spun. Emergence of the imagines (adults) may commence from October.