Brimstone Butterfly

(Gonepteryx rhamni)

By Rhodri Phillips

Identification: The Brimstone butterfly could be considered to be the original butterfly, with its green/yellow appearance giving rise to the term “Butter – fly”. Its large wings also function as an almost perfect form of camouflage, mimicking a leaf and its imperfections perfectly with brown spots completing the illusion. They can frequently be seen flying around open woodland and grassland areas, even feeding on road verges during the spring.

Life cycle: Their eggs start to hatch in May which is quite late for caterpillars to emerge. However, its timing is perfectly designed to coincide with the blooming of their chose food plant Buckthorn, which produces fruit in May and June. The caterpillars will feed on this plant until the end of July when they Cocoon themselves in a chrysalis to begin the transformation into the adult form of the butterfly.

Species importance: Due to their late emergence Brimstone butterflies play an important role as a late summer pollinator. Similar to bee’s, when butterflies feed off the nectar produced by plants they also transport pollen from one plant to another, enabling them to reproduce and survive. This is a key function in any terrestrial habitat, but they also occupy a vital role as a prey item for many birds and mammals. As such butterflies are a key indicator of an ecosystem’s health, with high numbers of the species a sure sign of a healthy habitat.

Conservation status: Currently Brimstone’s are doing well, with population numbers growing by about 20% in the last 30 years. However as a late developing insect species there is cause for concern as climate change starts to impact the worlds ecosystems more and more. Particularly wet or dry conditions could lead to a decline in the species as foodplants may be washed away or die due to extreme heat earlier than is usual. Despite this, the population growth of the species in the UK is still a positive sign.