Butterflies emerge as sun shines

The brimstone is one of the earliest butterflies to be seen on the wing. As I write, a bright sulphur yellow male is making the most of the early warmth, seeking out nectar sources in the garden. Despite its bright colouration the brimstone is often overlooked, perhaps because it is on the wing so early in the year, relegating it to a lower tier in terms of familiarity. The species is one of just a handful of butterflies to spend the winter in their adult form, along with comma, peacock and small tortoiseshell (from the common species) and large tortoiseshell and Camberwell beauty (from the rare visitors). To these can be added red admiral, a species now able to overwinter here successfully because of our increasingly mild winters. Resembling a dying ivy leaf, the brimstone is ideally camouflaged to spend the winter tucked away in thick vegetation; only venturing out once sufficient warmth is felt. Too early an arousal can be disastrous, with the limited fat reserves quickly depleted if energy is expended in a fruitless search for nectar that is not yet available.

Alongside the bright yellow males, whose colouration is thought by some to have given rise to the word ‘butterfly’, female brimstones may also be seen on the wing. Their colouration is a pale yellow green, reminiscent of the primroses that are in flower at the same time. These adults will remain on the wing through into June, possibly even early July, mating and then laying their eggs singly on buckthorn or alder buckthorn, the favoured food plants of their caterpillars. Unlike certain other species, which form distinct colonies, brimstones range widely and females will travel considerable distances in order to find suitable sites for egg-laying. The generation of adults that emerges from these eggs may be on the wing from late July or early August and will remain on the wing as the warmth of summer begins to fade through into autumn. This means that, successful hibernation allowing, some of these adults will reach 11 months of age, making the brimstone one of our longest-lived butterflies. Because it overwinters as an adult, the brimstone has to spend many hours in late summer nectaring, laying down the fat reserves that will get it through the winter ahead. Watch one feeding in your garden and you will quickly notice that it is able to utilise those flowers with particularly deep nectarines, like buddleia, teasel and runner bean.

So, while this butterfly may be seen on the wing in every month of the year, it is only really now, during early spring, that we tend to notice them; a real shame for such a spectacular insect.