Green-veined White Butterflies

These are common butterflies, closely related to the Cabbage White. Instead of laying their eggs on garden cabbages they prefer wild cabbages. Our oil seed rape field was fluttering with them this afternoon. There are two "flights" - those that hatch in April/May/June and those that hatch later in the summer. These two have more distinct veins so they are from the earlier flight. The wings are often pale yellow. Here the upper butterfly has less yellow than usual. The lower butterfly has much more yellow than usual - in fact it's much the same colour as the oil seed rape flowers that it was laid on - and it's probably the female. I've just read that the male smells like lemon verbena (who knew that butterflies had a scent?), but I was too busy trying to focus to notice its scent, and anyway the oil seed rape has a strong cabbage smell this time of year.