December Moths

Yes, there really are moths that fly in December. You might think that all moths fly on warm summer nights, which most do, but there are moths flying at all times of the year.  One of them is actually called the “December moth” and as the name suggests it flies mainly in December. Perhaps because of this habit of flying on rather cool nights, it comes with quite a shaggy fur coat.December moth

You can see that this male December moth has large feathered antennae, these are used to detect the female’s pheromones and so find her as quickly as possible. This style of antenna is shared with another of the moths of December, the appropriately named feathered thorn.feathered thorn

Like most other moths both sexes of the above species can fly. A number of other winter flying moths have females that are wingless or, more accurately, with such tiny wings that they cannot fly. This enables them to put as many resources as possible into egg production. There are several such species, one of which is the mottled umber, a very variable moth. Inevitably it is only ever the males that come to the moth light! The females wait on a tree trunk to be found by the males, who use the pheromone scent carried on the breeze to find them.mottled umber

The tactic obviously works as one of other species that also has flightless females is the winter moth, which is mostly about between November and January and is very common and widespread, it is even found on Shetland. In fact it is so common, that it seems that blue tits actually time their breeding so that their chicks can be fed on the huge number of winter moth caterpillars to be found on many species of tree in May.

These winter-flying moths are interesting, why do they fly in the coldest months? They cannot feed on nectar as many other moths do, as there are no flowers, actually not as much of a problem as it might sound as quite a few summer flying species do not feed as adults. But flying in the cold is more of a problem, their flight muscles need to be above a certain temperature to allow flight, so they mostly fly on the warmer winter nights, recent nights have been kind to them in this regard. A clear advantage of winter flight is that there are many fewer bats about and bats eat a lot of moths!

I have mentioned one of the advantages of having flightless females, they can lay more eggs. However you would imagine that being flightless would be a real drawback when it comes to dispersal, males can fly off, but this is useless if the females cannot move. Males might find ideal new habitat but they cannot colonise it without females. It is hard to imagine a caterpillar or an adult female walking more than the distance from one tree to the next in each generation, so a few metres each year, at that rate they would have not have spread more than a few kilometres since the ice receded and the land bridge to Europe was cut off! (assuming of course that they got to the land bridge at all). So how have they become so nearly ubiquitous across the UK?. It turns out it is the caterpillars that fly, they use a technique like that of spiders, known as “ballooning”. The small caterpillars go to a high point and produce a long strand of silk and get carried off by the breeze, sometimes for long distances.


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