For us it may seem too early to embrace the anticipation of a Spring in full throng but the humble Brimstone butterfly has no such notion; these summer wings often beat on a Winters breeze.
The Brimstone is one of the few British butterflies that overwinters as an adult, entering a period of dormancy in the coldest months alongside the Comma, Peacock, Small Tortoiseshell and, in good years, the Red Admiral. Nearly all of our other butterfly species spend the Winter as eggs, larvae or pupae. The key word here is ‘dormancy’ as strictly speaking no insect ‘hibernates’ in the truest, scientific sense of the word though we often speak of butterflies and hibernation regardless. This period of dormancy means that butterflies are highly susceptible to even the slightest changes in temperature and so on uncharacteristically warm winter days, above 10 degrees centigrade, Brimstones will again take to the wing.
Of course this revival in warm spells is often fraught with danger. Most overwintering adult butterflies will hunker down for the winter in cool, dry and sheltered spots such as log piles, outhouses and sheds. Inevitably some will venture into our homes and find a secluded position to rest up for the winter only to be awakened by the warm fuzz of our central heating, often kicking in on the very coldest of days. As well as the initial confusion, if the butterfly makes its way outside on the false promise of warmth and nectar only to find heavy rain, sleet or snow then the chances of survival are slim.
Regardless of the weather conditions, the Brimstone is often the first butterfly to emerge in the new year and brings much in the way of excitement, harbinger of the warmer days and lighter nights to come. The first of 2017 was recorded in Sussex on the tenth of January whilst vast swathes of the country (even Leicestershire!) were bathed in balmy 13 degree sunshine. This Brimstone wasn’t the first butterfly to spread its wings though; remarkably, on New Years day, Red Admiral and Peacocks were recorded in the southern half of England while just three days later a small Tortoiseshell emerged in Bedfordshire. Over the coming days and weeks, with temperatures set to slowly rise, I suspect that we will begin to see more and more Brimstones taking to the skies, at least in England and Wales.
The Brimstone is a notable absentee of the Scottish countryside but has recently spread north beyond its traditional fringe running between Cheshire and east Yorkshire. The adults will range widely in the search for food, commonly observed flying along roadside verges and hedgerows in search of knapweed and other nectar rich wild flowers. Potentially these roaming adults may be found in parks, woodland, scrubland, grassland and even gardens but that comes with a certain caveat; the larvae of the Brimstone feed almost exclusively on the leaves of Buckthorn and Alder Buckthorn which limits breeding to areas of chalky soil or damp scrub and woodland, wetland and moist grassland where these shrubs tend to be found more readily.
One of our more unassuming species of butterfly, the Brimstone is in my view highly underrated. The soft pastel green-white of the female is often mistaken for the Large White whilst it is the male that possesses the more easily identifiable warm yellow tone. Each wing is adorned with a small orange spot, whilst the underwing is greener in colour. The wings are exquisite in angular shape and strongly veined making them perfect camouflage against leaves and leaf litter when roosting at night. Whilst they may lack the instant impact of the Red Admiral, Painted Lady or the Peacocks all-seeing eyes and lashes of powerful, showy pigmentation it may come as a surprise to find that it is the humble Brimstone that gave butterflies their name; the yellow and pale white of the male the colour of butter, hence ‘butter-fly’.
If this mizzy rain finally ceases to fall and the temperatures rise by a couple of degrees, don’t be surprised to stumble upon the elegant flutter of the Brimstone in the coming weeks. Whilst we might not be on the verge of a rapturous Spring just yet, take comfort from the awakening Brimstones getting a head-start in the mad-dash Spring pursuit of a suitor and new life. Their detection of the growing warmth, even if we’re still in hats and gloves, should be enough to reignite the fires of Spring within.