August 2014

Peppered moth - Biston betularia

National Moth Night turned out to be somewhat damp and so Trevor and I postponed the moth trapping for a week or so and there were plenty of moths out there, including some magnificent hawk-moths, as well as some very much smaller micro-moths that are much more difficult to identify.  One of the difficulties in identifying moths is that some species have several different colour forms, the most famous example of this being the Peppered moth (Biston betularia).  We have Peppered moths in the moth trap quite regularly.  The most common form of this moth is white and it is ‘peppered’ with black dots, but it also has a completely black form.   Originally, most of the moths were the white form, with relatively few of the black form (less than 1%).  But in the nineteenth and early twentieth centuries, it was noticed that most of the moths were of the black form, in fact, by 1895 more than 95% were the black form.  This was because industrial and urban pollution killed the pale coloured lichens, and soot made the trees where they rest during the day, black.  This meant that predators could easily pick out the white form, but the black form was hidden against the black trunk.  Now that we have the Clean Air Act, the lichens have returned and the trees are no longer sooty, so the white form is more common – evolution in action indeed.

Field Grasshopper - Chorthippus brunneus

But moths are not the only creatures with different colour forms.  I recently photographed a pink grasshopper near Dungeness.  I got quite excited when I got back home and read that the pink form of the Meadow Grasshopper (Chorthippus parallelus) was quite a rarity when the normal colour form was green, or green and brown.  When I read a bit further though, I found that some experts think that all the nymphs of the Meadow Grasshopper are pink and that only the females in rare cases retain the pink colour to adulthood.  (Nymphs are the non-flying juvenile form of grasshopper which doesn’t have the larval or caterpillar stage of other insects.)  So of course all I had to do to prove that I had a rarity was to see if the grasshopper I photographed was a nymph or an adult.  I checked and it was indeed an adult, but while I was checking it, I noticed that though it was an adult, it was an adult Field Grasshopper (Chorthippus brunneus).  When I looked up the Field Grasshopper, I found that rather than different colour forms it has a range of colours from buff through green to purple, and that pink wasn’t at all unusual.  Ah well, it’s still a very pretty insect.

Another colour variation you may see if you are anywhere near the Village Hall is a white squirrel.  This is not a different species, but a white form of the Grey Squirrel (Sciurus carolinensis).  There are two reasons why a grey squirrel may be white.  One is albinism, this occurs when the animal has a genetic mutation that makes it unable to produce melanin, which is the substance that gives skin and hair its colour.  The other reason is called leucism and it is where the animal has a normal gene that codes for different fur colours in the same way that we have a gene for blue or brown eyes.  Because the gene is recessive, both parents would have to be white for the offspring to be white.  If one parent was grey then all the offspring would be grey.  The difference between albinism and leucism is that albino squirrels have pink eyes, whereas in leucism they have normal black coloured eyes.  The one by the Village Hall has pink eyes, so it is an albino squirrel.  According to wildlife experts there is a one in 100,000 chance of a grey squirrel being born white.  I've been unable to find out who those experts are, or to find out how they came up with such a suspiciously round number, but it’s a remarkable sight and I’m indebted to Trevor Buttle for the great photograph.

Grey Squirrel - Sciurus carolinensis