Every now and again nature throws up a strange aberration. Probably a single mutant gene produces a unlikely looking specimen.
This is the normal side of the moth I found in my MV trap this morning, and it is obviously a Silver Y (the commonest migrant each year).
This is the side that I saw first and it is quite different . To the eye it is darker with very little patterning, as is often the case, the digital sensor finds some patterning, but quite unlike the normal side.
From directly above the contrast between the two sides is very noticeable, and it is obvious that it it complete symmetrical, as if a line had been drawn down the middle of the moth using a ruler.
I turned it round to show that it isn't a function of the light. There doesn't appear to be any damage to the plain side.
From the underside the division in colour is even more striking. The two pictures show that the division neatly bisects the head.
Although it can't be seen here, even the scales on the legs were different on each side. I haven't yet found the name for this aberration, I'm sure it has happened frequently enough to have be named.