Winter Moth Winged Male and Wingless Female
In this article, Wildlife Matters discovers the fascinating life of the Winter Moth. In early December and throughout the Winter, you may come across 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 in the picture, you have found Operophtera brumata, whose vernacular name is the winter moth.
Some may know it as the Evesham moth because it was very prevalent in the orchards in that area of Worcestershire that it was considered a pest and the gardeners would put bands around the bottom of their fruit trees in an attempt to stop the Winter Moth from breeding. Kent’s orchards were also a magnet for the Winter moths and their voracious larvae. The Winter Moth has a very similar relative that is a little larger and paler called Operophtere fagata, its vernacular name is the Northern Winter moth. Both moths are common throughout Britain.
So, what makes this little Moth so special?
Well, firstly, the Winter moth is one of the very few moths that fly in sub-zero temperatures, although you are more likely to see it on milder nights.
Male Winter Moths are not powerful fliers but they do have wings, unlike the almost apterous females, having just vestigial apologies for wings. The females don’t need to fly because they crawl from their pupae when they mature and up the stems and trunks of trees and shrubs.
Whilst out one evening earlier this week, I was delighted to see a large group of moths in front of me, that appeared to be attracted to my head torch. Whilst the male winter moth is certainly attracted to lights, I realised that it was more likely to be the powerful pheromone that the flightless females waft into the breeze that was the reason for this large gathering of moths.
I was in broadleaved woodland, that was predominantly Oak. I approached a large Oak tree that was in front of me, a hugely impressive tree, standing perhaps 30 metres tall with a diameter of over 1 metre. I stopped and shone my light up the oak tree and that’s when I saw a spectacular sight. There were hundreds, possibly thousands of female winter moths, crawling down the ridged bark of this magnificent old oak tree.
The pheromones were sending the male winter moths into a frenzy of activity as they searched for females to mate with. It was truly spectacular to stand by the trunk of the Oak tree with the moths frantically flying all around me. I turned my head torch to night vision mode so as not to distract some of the moths from their objective, which was to breed.
These male winter moths would have emerged from their pupae, a day or two ago with their only objective in their short lives to breed. Not so easy when you have to find the female moths, that’s why the pheromones that float on the chilly evening breeze are so important. Once the males have bred their mission is complete and they fall to the woodland floor and die amongst the leaf litter.
It’s not the same for the flightless females. After breeding, she must climb up to the upper reaches of the tree, some 30 metres up in the night sky, where she will deposit her fertilised ova, maybe as many as 100 per female, into the budded shoots of the oak tree.
Winter moths are univoltine – they have a single brood in a year – and euryphagous, so their larvae will eat many plant species. Oak is a very popular choice but fruit trees are a particular favourite, and that’s why they were, and remain unpopular with orchard owners and some gardeners., but in the woodland, you will find them on birch, buckthorn, willow, hawthorn, hazel and many others.
Once the female has laid her ova into the buds of the host tree, she has completed her life’s purpose and she will also die. Of course, I wasn’t able to see the females as they were so high up the tree on this cold and dark winter evening, but I knew if I returned around sunrise I would know if the females had been successful.
So, before dawn the next morning I returned to the Oak tree and sat in the stillness and quiet of the morning, listening. After a short time, I could hear the slightly anxious sound of the group of long-tailed tits approaching through the canopy. They don’t sing like songbirds but have very distinct and definite sounds that the group used to communicate with each other. I sat, listening intently, not aware of anything but the ‘chattering’ of the long-tailed tits and the calming rhythm of my breath.
It didn’t take long for them to arrive, there were maybe 15 to 20 individuals, the sounds they made were distinct, the anxiousness gone to be replaced with an excited shrillness. They were soon in the upper canopy, speculatively scouring the branches for the dead female winter moths, which provide a protein, fat and fluid-packed food source that would help ensure this flock of long-tailed tits survived the chill winter months. Very quickly the initial flock were joined by others, including Great tits and Blue tits, and the morning feasting was in full flow.
But the winter moths don’t only provide for our native birds in the depth of the winter months. The moth’s ova hatch in spring after overwintering, and soon begin boring into the tree’s now swelling buds. The moth larvae consume the young bud for a while, before spinning a silk line and letting the spring breeze glide them to new branches where fresh new buds and leaves, as they emerge are waiting to be consumed.
Winter Moth Caterpillar
The winter moths larvae, like their parents, aren’t spectacular in colour, being fairly typical of a “looper caterpillar” type of the Geometridae, the family to which this species belongs. The larvae are mid to pale green with paler longitudinal green stripes.
Many birds, particularly, the tit family, will coincide their brood to hatch around the time the winter moth larvae emerge, as these caterpillars provide the nutrition and energy the young hatchlings will need to survive.
Keep an eye open in the spring for blue tits, amongst many other species, hopping around the trees in your garden. Local park or woodland. The trees will only be coming into leaf, so it is easy to watch the blue tits, busily jumping around the seemingly barren branches as they search for the caterpillars to feed their young.
The winter moth larvae emerge in their thousands and those that aren’t taken by the birds to feed their young will begin their descent of the tree back to the ground. Once on the ground, they will build themselves a silken chamber in the earth, perhaps a few centimetres down and it is there that they will begin to pupate. They will stay in their silken cocoon until October when they begin to emerge as ‘imagines’ – as they are so beautifully named as adults and begin the whole cycle of life again.
Nature is amazing. I hope you will take a little time from your busy lives to just stop and enjoy so of the spectacular creatures that we share our world with.
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