This is always a welcome find in the moth trap. It is not rare but it is a lovely little insect with superbly patterned wings that is just nice to look at. When newly hatched it is vivid green but the colours fade to a yellowish green after a few days on the wing.
The green carpet (Colostygia pectinataria )is a member of the Geometridae family. These moth are generally triangular in shape when at rest, hence the link to geometry. It helps with identification to look for family features.
This moth is flying here in Dorset from late May through to the end of July and then we may get a second brood in the autumn depending on the weather. It widespread and quite common although not a great visitor to light traps.