The brimstone is one of the earliest butterflies to emerge from hibernation, and may be seen on mild February days – keep an eye out for your first brimstone of the year when the sun shines and it feels like spring, out of the corner of your eye you might spot one, flying at speed at the edge of woodland or a bank of trees. Sightings peak in April, however, when spring is in full swing and there are plenty of flowers to feed from. The male is a bright buttery yellow – it’s thought the word ‘butterfly’ can be attributed to the ‘butter yellow’ of the male brimstone – while the female is paler, almost white. Both sexes have a small orange spot on each wing.
Found throughout the British isles but rare in Ireland and Scotland, the brimstone feeds on a variety of flowers, such as dandelions, chives, red clover, wallflowers, buddleia, scabious, red campion and Verbena bonariensis. Mating and egg-laying take place from May to June, typically on leaves of buckthorn (Rhamnus cathartica) and alder buckthorn (Frangula alnus). Caterpillars are found from June to July and are well camouflaged. These caterpillars pupate and emerge in August, when the second peak of sightings occurs, before hibernation begins.
The brimstone hibernates as an adult, typically behind stands of ivy or other evergreen plants like holly. It is perfectly camouflaged as its wings resemble that of a leaf.
How to help brimstone butterflies
You can help brimstone butterflies at all stages of their lifecycle by growing buckthorns. Alder buckthorn is best for acidic soil, while purging buckthorn is best for chalky soil. Grow a hedge of buckthorn in full sun for the best chance of success, and don’t trim it in summer to avoid accidentally disposing of brimstone caterpillars.
For adults emerging from hibernation in spring, fill your garden with spring flowers such as primrose, wallflower, dandelion, cowslip, bugle and bluebell. Then, in summer, grow devil’s bit scabious, teasel and betony.
For hibernation, avoid cutting back your ivy and ensure there is plenty of scrubby material for them to hunker down in.
