Now you see it, now you don't

I accidentally disturbed this silver Y moth Autographa gamma and watched it fly across the garden and then settle. I thought I had pinpointed the spot where it landed but when I went to have a look I couldn't see it at first. It's camouflage was amazingly effective against a background of dead Anchusa leaves and dead wood. 

Melanic magpie moth caterpillar

More photos from the 1990s found in the back of a cupboard.

Every few years our garden gooseberry bushes are infested with magpie moth caterpillars. They're hard to miss, with this gaudy black, white and red colour scheme which is a form of warning colouration (aposematism), warning birds that they are foul tasting: the theory is that any bird eating one would remember not to eat these colourful but distasteful caterpillars again.

One infestation included this all-black melanic mutant magpie moth caterpillar. 

Industrial melanism, where mutant black forms of the pale grey peppered moth Biston betularia appeared and rapidly increased in frequency, is one of the classic textbook examples of natural selection in action, based in crypsis. In that case the melanic form provided better camouflage against sooty tree trunks in industrial cites, was less frequently predated by birds than the pale grey form and so rapidly increased in frequency. When air quality improved in cities and the soot disappeared from tree trunks the melanic form became more conspicuous and vulnerable and the better camouflaged pale form increased in frequency again.

With this melanic magpie moth caterpillar the selection pressure is quite different because this insect larva benefits from being conspicuous and warning birds of its unpalatability. Losing its bright colours ought to be a distinct disadvantage. 

Maybe that's why, in the 20 years since I took this photograph, I've never seem another melanic magpie moth caterpillar on our gooseberry bushes.

Silver Y

This hasn't been a particularly good year for the silver Y moth Autographa gamma numbers in my part of County Durham. In some years many thousands migrate here from the Mediterranean early in the year and by now, after several generations of breeding, the Michaelmas daisies and Buddleia x weyeriana in the garden would be smothered in them. It's only now that a few are appearing on a daily basis, just as the frosts begin. The cool, wet summer may be to blame. 

Silver Y moths are restless insects, never coming to rest while they feed, so it can be difficult to appreciate the beauty of their mottled wings. But after a cold night they are more accommodating, resting head downwards, waiting for the sun to warm them up. Today Martin Wainwright, over at Martin's Moths, has some fascinating information on the way that moths go through their pre-flight warm-up routine.

We found this silver Y early yesterday morning on a dry stone wall high in the Pennines, 400 metres asl on Chapel Fell where the grass was still covered with frost. The mottled wings provide excellent camouflage on a lichen-covered rock and my wife only spotted it because it had begun to shiver, as part of its warm-up.

When we got home we found another that had spent the night on our window, probably attracted to the room light last night and again resting head down. No effective camouflage this time, but from this angle the irregular outline of the dorsal side of the body is evident - all part of the crypsis in profile as well as plan view if the moths land on a suitably matching background.

In a good year there would be vast numbers of silver Y moths on the wing now and Africa Gomez, over at her excellent BugBlog, describes how it has recently been discovered that they are capable of migrating south, all the way to the Mediterranean with a favourable wind, to escape our winters which would kill almost all of them.

You can find another picture of a silver Y feeding here