The Brimstone butterfly is one of the most welcome harbingers of spring and is believed to have created our word 'butterfly' from its early description as 'the butter coloured fly'. It hibernates as an adult, normally deep in ivy or brambles, and is probably our longest-lived butterfly. An adult, emerging from the new brood in late July or early August, then successfully hibernating can still be flying the following summer. The male's deep yellow colour is only likely to be confused with the much rarer migrant, the Clouded Yellow, but the female is lighter, with more of a greenish tint. It can be confused, at a distance, with the Large White, though the wing shape is different. I mention this since I'm obviously aware of the Large White's reception in many vegetable gardens..
To produce the summer generation the small, off-white, bottle-shaped eggs have to be laid on its sole food plant, the Buckthorn. Two varieties, Purging (Rhamnus catharticus) and Alder (Frangula alnus), are used, but the latter is normally preferred and is more suited to Suffolk conditions. It is the one plant habitually overlooked in many planting schemes, especially hedges, based on native species, but is now thankfully more widely available. It needs to be placed in a situation where there is an abundance of sunlight for most of the day. The Brimstone's tenacity in seeking out its food plant is legendary. As a recent example, the Suffolk Branch of Butterfly Conservation visited, in early June 1988, a farm at Polstead which won first prize in a recent FWAG conservation competition. The farmer had planted Buckthorn especially for the Brimstone but admitted he had been too busy to check them. Our group found seven caterpillars, well camouflaged by their colour and habit (when not feeding) of lying along the midrib of the leaf. Traditionally the distribution in Suffolk shows a bias towards the west of the County, which presumably has more Buckthorn. Consequently any additional local planting will be most helpful. The Brimstone is not a rare Suffolk species but, compared to the three others hibernating as adults, it certainly needs some help: Suffolk has 1085 two km. tetrads and, at the start of 1998, the Brimstone had been recorded in 383, compared to the Comma (488), Peacock (752) and Small Tortoiseshell (862).
The Ipswich Organic Gardening Group and the Ipswich Wildlife Group have started a campaign to make Buckthorns available. Buckthorns can be grown in most gardens and like dogwood, is a colourful addition to either the shrubbery, or the wildlife patch. Buckthorn was once used as a laxative and it is recommended that it not be planted where livestock or young children could possibly eat some of it.
The initiative will monitor the condition of buckthorns planted under it for evidence of Brimstone caterpillars, with the results being given to the Suffolk Branch of Butterfly Conservation. There is a slight charge of 50p per plant to offset costs. Contact Julian Dowding on 01473 414 092 for more information.
Richard Stewart