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The December moth

David Chapman / 08 December 2016

Wildlife expert David Chapman introduces the December moth, one of the few British moths whose adult form can only be seen in winter.

December moth
December moth

Winter might not be the best time for spotting insects but there are some which can only be found in winter, despite the obvious difficulties that must cause them.

How moths and butterflies survive British winters

Being cold-blooded and small-bodied insects have developed a number of clever strategies to survive the winter months in the UK.

The life cycle of moths and butterflies, for example, comprises of egg, larva, pupa and adult, so one of those forms must be adapted to allow the creature to survive over winter.

One or two species have developed an avoidance strategy. In Britain we have some migratory species such as the painted lady butterfly, which moves from Morocco to Northern Europe in the spring then back again in the autumn, and silver-y moth, made famous by its invasion of the Euro 2016 finals on its northern migration early in the summer.

Most moths and butterflies that live out their entire lives in Britain survive over winter as larvae, a form which we often refer to as caterpillars.

The next most common strategy is to lie dormant as a pupa, many larvae choose to bury themselves underground before pupating to try to avoid the lowest temperatures.

Some moths and butterflies survive the cold months in egg form whereas some lie dormant in adult form.

We have a few butterflies such as the red admiral, small tortoiseshell and peacock which can survive the winter in adult form and probably the most famous moth adopting this approach is the herald moth which often resides in houses and out-buildings.

These ‘hibernating’ moths and butterflies try to lie dormant as much as they can through the winter months and become more active in the spring and more numerous in the summer.

In contrast there are some true winter specialists, some moths which can only be found in their adult form during winter. These include the winter moth (seen on the wing from October to January throughout the British Isles), the spring usher (seen on the wing from late January to March) and the December moth.

Find out what to do when you disturb hibernating insects

When to spot the December moth

The aptly named December moth can be seen on the wing mostly in November and December. It is common throughout England and Wales, even being found in lowland Scotland.

The adult December moths lay their eggs on twigs and branches of trees and that’s how they survive through the remainder of the winter, with eggs hatching into larvae during spring.

December moth diet and habitat

They are found in woodland, along hedgerows, in scrubland and gardens where its larvae feed on the leaves of a variety of native broad-leaved deciduous trees and shrubs including oak, birch, hawthorn and blackthorn.

Fortunately December moths are attracted to lights and that is how I usually see them. The white wall below our outside light is a magnet for them.

This is a small moth with a wing span of between 30 and 45 millimetres, females are larger than males. Both male and female have a charcoal wings with creamy-white markings.

How December moths survive winter

Insects such as the December moth can survive in adult form over winter by using a number of strategies.

Within their bodies these insects have alcohols which act like ‘anti-freeze’ to stop ice-crystals forming. They can also expel water from their system to prevent their insides from freezing.

In order to become active they will vibrate their wings to generate their own body heat, allowing them to fly on cold nights.

The December moth belongs to the family ‘Lasiocampidae’ which includes the larger, and probably more familiar, eggar moths.

None of the moths in this family is able to feed so once they have emerged from their pupae they are on borrowed time, using the energy stored when feeding as a larva.

Their purpose is to disperse and find a mate. When you consider the lack of nectar sources available in the winter this is another very important adaptation of the December moth!

Find out more about British moths

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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.