Migration wave

Several days ago, we had a mini-invasion of white butterflies. Most were the resident Small Whites (whose picture I haven't yet managed to snap), but a few were immigrant Large Whites (Pieris brassicae) like this one, driven north by the gentle southerly winds that had been blowing for days. The broad black tip to the upperwing, particularly how far it extends down the back edge of the wing, helps to distinguish this species from its smaller cousin, while the dusting of dark scales on the underside of the hind wing and the bold black spots on the upperside of the forewing mark it as a "first brood" female. Unlike some British butterflies, Large Whites have multiple broods per year. They fly from March to late October, and occur throughout the British Isles; elsewhere, they're common and widespread across northern Africa and all of Europe, the Middle East and in Asia as far as the Himalayas. Their diverse habitats include virtually anywhere their larval host plants occur, and adults are particularly fond of thistles and knapweeds.

As larvae, Large Whites can become serious pests of Brassicaceae species, including cultivated crops such as broccoli, cauliflower, kale, mustards, horseradish, etc. While their damage tends to be fairly limited in Britain, they are capable of causing the near-complete loss of crops in localised areas elsewhere in the world. Fortunately, none of our neighbouring farmers have planted such crops this year, and we don't much care what they nibble here in the garden — within reason of course!