Common and becoming more widespread  and abundance determined by the presence  of one of its larval foodplants .  It is a strong , fast flying,  far ranging species that can turn up in almost every corner of our county.  However they do come together to form colonies often in woodlands where they will overwinter.   The species is not under threat.

Our only large yellow butterfly and similar in size to a Large White  and with same purposeful strong directional  flight.  It  spends little time fluttering unlike the other whites. Only the male is citrus yellow, the female being pale green but both sexes have a orange spot in the centre of both fore and hind wings which you can glimpse in flight.  Occasionlly you can glimpse the  characteristic points on each wing . However the main diagnostic feature  in flight is the  female is the palest shade of green while the large white a pale cream.

 When not in flight they always have there wings shut.  Both sexes have a pale green underside with realistic cryptic leaf like viening and even brown spots of leaf damage.  The head, antennae and eyes are a rich dark burgundy. Both hind and forewings have a characteristic point, like a leaf tip, and can literaly disappear in front of your eyes when it lands to rest beneath a leaf.  

Adults  spread widely so it is not surprising we see them but finding their rare foodplant necessitates constant searching.  After wintering in woodlands  males emerge first and  hunt for females.  Eggs are placed on leaf buds at the shoot tip and the underside of the youngest developing leaves of foodplant leaves .  At first blue through green and then later pale cream  bottle-shaped eggs are quite conspicious  and are only laid on Buckthorn species.  

Females will spend time testing the plant selecting those in  fairly good light and healthy and she will return many times  over the spring monthes into summer.   They tend to choose smaller plants away from others in an attempt to avoid predation by  particularly blue tits  who will home in bigger plants with more caterpillars. Mortality rates can be very high. 

Eggs are laid from April to July and hatch after about 10 days.  At first pale pale yellow larvae feed on the underside of the youngest leaves  but rapidly grow  and later instars are darker green larvae take around a month and 5 instars to mature and usually leave their buckthorn to pupate in low vegetation.  

Adult butterflies emerge after about 2 weeks and can remain active until the end of Sept or later, returning to their woodland  home then can re-emerge to take advantage of good conditions to build up reserves. In very hot years they rarely reappear unless nectar is abundant.  

The species shows a strong preference for purple flowers when nectaring, and its long proboscis is well-adapted to feeding on flowers like Teasel Dipsacus fullonum.  Brimstones often hibernate under evergreen leaves, especially Holly or Ivy.  They may 'test' the air on warmer winter days and visit ‘Pussy’ Willow catkins Salix sp or early Dandelions  in search of a top-up nectar feed.  

NF              12/11/20