The brimstone, Genopteryx rhamni, is a large butterfly found across Europe, Asia, North Africa, and in the UK.
It is not rare and here on the Island is widespread in woodlands where buckthorn and alder buckthorn, its larval food plant, grow.
It is single-brooded and hibernates as an adult, usually in dense ivy or bramble thickets for up to seven months.
To survive in winter, their internal bodily fluids contain glycerine, forming a type of antifreeze that gives them protection down to -20°C.
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The butterfly emerges in early spring to search far and wide for a nectar source, which is when they can be seen almost anywhere, not necessarily in woods.
It is our longest-lived butterfly and can live for up to a year if conditions are suitable.
The males are a distinctive yellow colour and the females, by contrast, are a paler, more greenish white, but still fairly easy to identify, although their wings can look like leaves at first glance.
Both sexes have a small orange dot on each wing.
To be certain of seeing one, look for them during spring in Parkhurst Forest, Borthwood Copse, or Walter’s Copse at Newtown, all of which, in most years, hold good-sized populations.
Brimstone is an ancient name for sulphur, which is a bright yellow non-metallic solid found in hot springs and near volcanoes, its colour thus giving the name to the butterfly.
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In the time of the early naturalists, butterflies were just called ‘flies’ and it has been suggested that the colour of the brimstone gave rise to it being called the ‘butter-coloured fly’ and then the term was used for all the insects that we now know as butterflies; it’s a nice thought but not necessarily accurate, we just don’t know for sure, Old English for butterfly is buttorfleoge, almost identical.
The scientific name comes from gonia meaning angle, pterux, a wing from the points on the outer edge of the forewing and hindwing and with rhamn being the name for the larval food plant, buckthorn.
In folklore, the brimstone symbolises transformation and resurrection with the coming of spring (its early emergence), longevity (its long life), happiness and renewal.
"If you smile when you see a butterfly, you have happiness in your soul," Diana Cooper.
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