Assynt’s Winter Moths

March 19th 2019

Many people might think that moths are too delicate to spend the winter as adults in our northerly latitude. However, for some, this is their flight period when they mate and lay eggs. The appropriately – named December Moth was attracted to the outside light of my house in Torbreck, near Lochinver (NC 085242), on 1st December 2018. It is a member of the family Noctuidae, most of which are powerful flyers with stout bodies.  This specimen was a male, displaying a magnificent set of feathered antennae (photo 1).  The males of many moth species have large comb-like antennae, which are used to detect the pheromones released by unmated female moths.  In the case of the December Moth, the females resemble the males.  Like other moths with a winter flight period, they lay their eggs on deciduous trees.

You may see the Winter Moth caught in your car headlights, flying weakly in sheltered places near woodland, while the Northern Winter Moth may be attracted to your outside light, as it was at my house on 1st December 2018. The males of these species are rather dull (photos 2 & 3), but, interestingly, the females are flightless – a condition known as “brachypterous”.  Their wings are reduced to stubs and are held over their backs as if being dried in the normal way (photo 4).   They are normally found crawling up the trunks of deciduous trees. On 29th December 2018, seven male Winter Moths were at lighted windows at Calltuinn in Nedd (NC 137319).  

The male Pale Brindled Beauty (photo 5) normally flies from January until March, but this one was a little early, again at my outside light on 1st December 2018.  In his book “Enjoying Moths”, Roy Leverton recalls finding a male encased in ice. He took it home, thawed it out and it flew off that evening.  Again, the females of this species are flightless, the wings being reduced to tiny stumps.  Surprisingly, a female was found indoors at Calltuinn, Nedd, on 22nd February 2019 by Ian Evans (photo 6).  The adult moth could have crawled in through a small open window, but Roy Leverton suggests that it may have come in as a caterpillar and pupated indoors, later hatching out.  Normally, females of this species are found near the base of deciduous trees just after dawn.

More recently, on 28th February 2019, a male Dotted Border was found on the outside of a window at Calltuinn, Nedd, by Ian Evans (photo 7).  This is yet another species where the females possess stumpy wings and eggs are laid on tree bark. 

The Winter Moth, Northern Winter Moth, Pale Brindled Beauty and Dotted Border all belong to the family Geometridae, the males having slender bodies and broad, triangular wings.  Since the females of these species have vestigial wings, they walk to lay their eggs instead of flying and so use less energy.  This enables them to remain active on cold winter nights.  They can also hide in crevices more easily and are thus less likely to be predated than males.  The caterpillars hatch from the eggs just as the new leaves appear on the trees.

Gwen M. Richards

References:  Leverton, Roy. (2001). Enjoying Moths. London: T. & A.D. Poyser.

Waring, P. and Townsend, M. (2004). Field Guide to the Moths of Great Britain and Ireland.  Hook: British Wildlife Publishing.      

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