The Delightful December Moth

The December Moth, Poecilocampa populi, is found all over the UK. Because it is more resistant to cold than most other moths, the adults are common in parks, gardens and woodland during late autumn and winter.

Marvellous Moths

Many people don’t give moths a lot of thought. Most have incredible camouflage and they often fly at night, so we don’t tend to see them. When we do think of moths, it may be just as a kind of drab butterfly that sometimes eats our clothes. In reality, there is much more to the world of moths than we might think, and they are very important to our world.

Moths, together with butterflies, belong to the group of insects called the Lepidoptera (“scaly wings”) There are over 2,500 species of moth in the UK and only a very few will eat our clothes. Many of these moths are beautiful, either because of their spectacular colouration or because of the way their camouflage enables them to blend into their habitat.

Moths are important in ecosystems. Both adult moths and their caterpillars play crucial roles in food chains, feeding on plants and being eaten by bats, birds and other animals. It is estimated that about 35 million caterpillars are eaten by blue tit chicks every year! Moths also play a vital part in the reproduction of several plant species because of their role as pollinators.

‘Like a moth to a flame’

December moth showing black and brown colouration.

Adult December moths are night-flying and, like other moths, they are attracted to light at night. Entomologists are still not sure exactly why this is. One theory is that moths use the moon to navigate and can mistake a light for the moon. Another is that they normally fly with the lighter sky above them and a light source near the ground confuses them into flying downwards. This would explain why they are attracted to street lights and lit windows, and also why they fly downwards into light traps.

December moth, Poecilocampa populi. Photo: Ben Sale CC-BY 2.0

Life Cycle of the December Moth

Larvae and pupae of the December moth
Larvae and pupae of the December Moth in the HOPE Collection at the Museum

While adult December Moths can be found throughout autumn and winter, each individual is short-lived and does not feed. They mate and the females lay their eggs on food plants. The eggs overwinter and the larvae only emerge the following spring. These caterpillars can be found throughout spring and summer taking advantage of the new growth of leaves. They are active voracious feeders at this time and will eat the leaves of a wide range of deciduous trees. When they have gained enough weight, they pupate, with the adult moths emerging to repeat the cycle in late summer and autumn.

Pinned adult DEcember moths in the HOPE collection.

Moths are important indicator species: their presence tells us about the overall health of the environment.  Unfortunately, what moth populations seem to be telling us is that something is wrong.

Comparing the number and type of moths found in Britain today with those recorded in historic insect collections like the HOPE Collection at the Oxford University Museum of Natural History, shows us that moths have declined by about 40% in southern Britain. Over 60 moth species have become extinct in the UK over the last century and many more are at risk of disappearing forever.

Other animal species which rely on moths as food are also suffering, including a decline in bats flying over farmland and reduced numbers of cuckoos, which specialise in feeding on hairy moth caterpillars which other birds tend to avoid.

We need to do more research to fully understand exactly why moth species are declining in Britain, but it is likely to be because of a combination of factors including loss of habitat, farming practices such as clearing hedgerows and the use of pesticides, and climate change.

Adult December moths in the HOPE Collection

Ways we can help moths

Fortunately, many moth species under threat are found in parks and gardens, so we can all do things to help:

  • Not over-tidying gardens; a more natural look is much better for insects.
  • Growing a wide variety of large and small flowering plants and, if you have room, shrubs and trees.
  • Avoiding the use of weed killers and insecticides.
  • Reducing light pollution from outdoor lights
  • Reducing your carbon footprint, for example, by driving less and walking or cycling more.

If you enjoyed reading about the December Moth, you might like this post by Ben on Raising Poplar Hawk Moths.

Raising Moths

Ben brought in some Poplar Hawk Moths to show the other participants at our recent summer school. Here he describes how he raised them from eggs he received as a gift from his grandfather.

Last year during lockdown my Grandpa gave me 32 hawk moth eggs: 30 eyed and two privet. Not the most common of presents you might think, but these turned into the most enjoyable gift. I was very excited as I tore open the parcel and found the eggs safely packed in a small tube. It took roughly a week for the leafy-green eggs to turn into the most delightful little caterpillars. I decided to call them all Jim. The first thing they went towards was the fresh willow that lay in a small, water-filled jam-jar.

Poplar Hawk moth caterpillar with Ben’s hand for scale. Photo credit: Ben Atwell

Immediately, they started taking chunks the size of their heads out of the leaves until there were no leaves left inside the tank. I was very surprised by how much they ate in proportion to their size. Every day they grew bigger until, within 4 weeks, they were the length of my index finger! They were bright green with white stripes, pink spots and little pointy tails. To help them grow, they shed their skins every few days. Sadly, one little Jim got stuck in his skin whilst shedding and died. Willow-collecting took a lot of effort as it involved daily trips to the canal, but this was a welcome break from staring at my computer all day during online school.

Poplar Hawk Moth larva feeding. Photo credit: Ben Atwell

One morning we found that a lot of the caterpillars were wandering around, banging their heads on the bottom of the tank. They were also turning a darker green which (after a bit of research) we found out meant they needed to bury and become a chrysalis. We put a deep layer of soil into the tank and within minutes they had disappeared. We tucked them up in the shed for winter and waited.

After months of hibernation, they started emerging this spring with crumpled wings, looking very like dead leaves. After stretching out their wings we noticed that we couldn’t see the eyes that the eyed hawk moths are known for, but as we later realised, they only show the eyes as a defence mechanism if they were under attack. Normally it would take a while for the males to seek out the females using their fanned antenna, but because they were in a large tank, it was easy for them to find each other and mate. Within a few days they had laid over 1,000 little green eggs! So, the process of willow collecting began again, but this time, after checking with the county moth recorder, we released the little caterpillars (who this year I called Jeff) into our local wildlife reserve, hoping that they survive and go on to repeat the process in the wild this year.

Poplar hawk Moth adult. Photo credit: Ben Atwell

We are still waiting for the privet chrysalises to hatch, but to keep me busy, my Grandpa sent me 15 poplar hawk moth eggs this spring. These have already been through one cycle of eggs-caterpillars-chrysalis-moth-eggs and I gave some of the eggs to the museum during the Insect Investigators Summer School. I hope the staff have time to collect all that poplar!

The Poplar Hawk Moth, Laothoe populi, is a beautiful insect found thrououghout the UK and is common wherever their foodplants can be found: mainly the poplar trees from which they get their name, aspen and willows. Ben describes the voracious appetite of the larvae well. The adults don’t feed at all and so are short-lived. You can find the adult moth from May to July and the caterpillars from June to October. In Southern England there may be a second generation of adults in the autumn.

Dr Andrew Salisbury

Dr Andrew Salisbury tells us a bit about his work at the Royal Horticultural Society (RHS), the world’s leading gardening charity. He also shares how he first became interested in insects, as a child.

He mentions a particular memory of an encounter with a Brown-tail moth caterpillar. Do you have any specific memories of insect encounters? Tell us about them in the comments below.