One of our gardeners sent me an image of a butterfly that he wanted to confirm the identity of. We know it’s a butterfly, because it rests with its wings upright and together. Moths lay them flat, so you can see the upper side.
Here is the one in question
This particular butterfly breeds very early in the year, in April and May. When this individual opens its wings, it’s white, with a black spot in the top corners, rather like a small cabbage white butterfly, to which it’s related. But, in this case, that tells us it’s a girl butterfly. The boy butterflies have a bright orange tip to their forewings. It’s an Orange Tip. Even in this position, with the wings upright, you can tell, because nothing else has exactly this green marbling effect that you see on both the boys and the girls.
Right now, they are waiting.
They are waiting for their caterpillars’ food plant to flower and set seed. Egg-laying has to be very carefully timed, because the caterpillar eats almost nothing else – it’s Alliaria petiolata, or Jack by the Hedge, Hedge Garlic, Hedge Mustard, whatever common name you’re used to.
This native wildflower has leaves that smell faintly of garlic when crushed, especially the young ones. You can use it in cooking or in salads. But these caterpillars aren’t after the leaves. They feed on the seed pods. The parents need to ensure that the plant they lay eggs on has a good crop of seed pods to come, and new pods that are young enough for the newly-hatched caterpillar to eat.
Jack by the Hedge is a member of the Brassica family, like rocket, or radish, or cabbages, and ornamentals like aubretia and honesty. Lacking their food plant, caterpillars have been known to feed on honesty seed pods, but success is poor.
I said it eats almost nothing else. The female butterfly usually lays only one egg per plant, because if there is more than one caterpillar per plant, they will eat each other, so they’re not all sweetness and light, it has to be said.
They will feed on the developing seedpods for about a month, and then they will pupate. They will find a suitable place to spin a silken thread to attach themselves to the chosen bit of vegetation. Then, apart from a small node of nerve cells, they will break down their caterpillar bodies into a sort of primordial soup, and reassemble themselves into a butterfly. They will stay as a pupa until next spring, when they will once more start patrolling, looking for a suitable mate and suitable food plants.
It’s a precarious existence. Each butterfly has survived as a single egg, as a caterpillar, and almost a year as a pupa.
So, do check that white-flowered plant that looks a bit like honesty before you weed it up. They need all the help they can get.