But­ter­fly with leaf-like wings

With its leaf-like wings, the sight of the Brim­stone but­ter­fly is all the more re­ward­ing among spring’s fo­liage

Landscape (UK) - - Contents - ▯ Words: Stephen Moss

on a warm April day in a sunny cot­tage gar­den, a glim­mer of yel­low wafts softly over the rich pur­ple blooms of an aubre­tia spilling from a dry­s­tone wall. This silent dancer is a Brim­stone but­ter­fly, its name an al­ter­na­tive word for sul­phur and one which re­flects the bright lemon hues of its leaf-shaped wings as it flut­ters from flower to flower. On set­tling, the but­ter­fly closes its wings, re­veal­ing their green­ish-yel­low un­der­side, and uses its long pro­boscis to feed on the en­ergy-giv­ing nec­tar be­fore flit­ting onto the next bloom. Af­ter feed­ing, it will rest, wings open, tak­ing ad­van­tage of the sun’s warm­ing rays. The Brim­stone, Gonepteryx rhamni, is one of the first but­ter­fly species to ap­pear in the spring. For the past six to seven months, this in­di­vid­ual has been in a state of tor­por, hav­ing re­duced its en­ergy lev­els so that it does not need to feed. It has been hid­ing away in a nearby wood­land, be­hind thick green leaves. Now that the air tem­per­a­ture has risen, and the hours of day­light are grow­ing longer from day to day, it is time for this hardy but­ter­fly to re­sume its life cy­cle again. The Brim­stone is one of the larger Bri­tish but­ter­flies, with an over­all span rang­ing from 2½-3in (6-7.5cm). The wings of the males are lemon-yel­low above and yel­low­ish-green on the un­der­side, and they have a grey­ish-white body. The fe­males are a paler green, so may be eas­ily missed when at rest among fo­liage. Both males and fe­males have lines, or veins, cross­ing their wings and or­ange spots in the mid­dle of each up­per

wing, which also help to con­ceal them from preda­tors. Brim­stones, like other but­ter­flies, are pre­dated on by a range of dif­fer­ent birds, mam­mals and in­sects, es­pe­cially wasps. For this rea­son, they have evolved a range of dif­fer­ent ways to cam­ou­flage them­selves through­out the dif­fer­ent stages of their life cy­cle: as eggs, cater­pil­lars, pu­pae and adults. They are also par­a­sitised by two species of wasp, each of which tar­get only this par­tic­u­lar but­ter­fly.

Var­ied habi­tats

Brim­stones are of­ten found in woods where, on bright, sunny days, they will fly along the edge of clear­ings and wood­land rides or wher­ever the sun pen­e­trates through the for­est canopy. They can also be seen along ma­ture hedgerows, at the edge of farm­land, es­pe­cially where a bor­der of grass and flow­ers has been left to thrive, and in rough grass­land. Another good space to spot them is along road­side verges, which, be­cause they are of­ten left un­sprayed with chem­i­cals, have more wild­flow­ers than much of the sur­round­ing coun­try­side. Like sev­eral other but­ter­flies, the Brim­stone is a fre­quent gar­den visi­tor, es­pe­cially where there are plenty of flow­er­ing plants on which the adults can feed. The Brim­stone has a fairly wide range and can be found across most of low­land Eng­land and parts of Wales, hav­ing spread north­wards into north­ern Eng­land in re­cent decades, prob­a­bly as a re­sult of warmer sum­mers caused by cli­mate change. How­ever, this species is rare in Scot­land and thinly-dis­trib­uted in Ire­land.

“Though the thicket’s bushy dell Tempts thee to the fox­glove’s bell, Come but once within my bounds, View my gar­den’s airy rounds, Soon thou’lt find the scene com­plete, And ev­ery flowret twice as sweet” John Clare, ‘To the But­ter­fly’

Like many other com­mon Bri­tish but­ter­flies, their num­bers have fallen in re­cent years: the UK pop­u­la­tion has al­most halved since the 1970s. This is mainly due to the de­struc­tion of hedgerows. World­wide, how­ever, the com­mon Brim­stone has a wide­spread dis­tri­bu­tion, be­ing found in suit­able habi­tats through­out the tem­per­ate re­gions of Europe, Asia and North Africa, so it is not en­dan­gered on a global scale. Brim­stones are able to spread be­cause they are strong fly­ers, with the abil­ity to live in a wide range of habi­tats. How­ever, they are lim­ited by the food plants on which their young feed: com­mon buck­thorn and alder buck­thorn, both of which are found in damp wood­land, while com­mon buck­thorn can also grow on chalk and lime­stone grass­land, and around wet­lands.

Courtship and breed­ing

Most Brim­stones emerge from their win­ter hid­ing places in early spring, gen­er­ally late March and April. But they may ap­pear on warm days as early as Jan­uary or Fe­bru­ary, and oc­ca­sion­ally even as soon as New Year’s Day, mak­ing them one of the first but­ter­flies to be seen each year. The males ap­pear a few days ear­lier than the fe­males, al­low­ing them to feed and build up their strength be­fore mat­ing. Hav­ing emerged, both sexes will feed on the nec­tar of dan­de­lions, prim­roses and blue­bells for a few weeks, be­fore be­gin­ning their courtship dis­play. This in­volves the male fly­ing up into the air and back down again, the two then flut­ter­ing around one another to ce­ment their pair bond. Once they have paired, the male and fe­male will mate, cop­u­lat­ing for up to 48 hours. They are monog­a­mous and, hav­ing mated, will not at­tempt to pair up with another part­ner.

In May, the fe­male lays her eggs, one by one, on the un­der­sides of the leaves of buck­thorn and alder buck­thorn plants, plac­ing a sin­gle egg on each leaf to min­imise the chances of them be­ing eaten by birds. She will try to choose only un­dam­aged leaves, as any holes may in­di­cate the pres­ence of other Brim­stone cater­pil­lars, which could, in turn, at­tract preda­tors. The eggs are ap­prox­i­mately 1.3mm long, 0.5mm wide and shaped like a skit­tle. When laid, they are green­ish-white. Over the next week or two, they grad­u­ally change colour, turn­ing first yel­low, then brown, which in­di­cates that they are ready to hatch. When the cater­pil­lars emerge from the egg, they are just 1.7mm long. How­ever, they grow very rapidly, as they feed vo­ra­ciously on the buck­thorn leaves, and un­dergo up to five ‘in­stars’, the pe­riod be­tween moult­ings, when they shed their outer layer to en­able them to grow. By the time they are fully grown, af­ter a fur­ther five to six weeks, they will have reached a length of 1½in (3.5mm). Brim­stone cater­pil­lars are mainly green in colour, with white hairs and small black mark­ings, which help to break up their out­line and con­ceal them as they feed on the top sur­face of the leaves. Once the cater­pil­lars reach their full length, they pu­pate, a stage that lasts for ap­prox­i­mately two weeks. The pu­pae are just un­der 1in (25mm) long, and green in colour, so that they re­sem­ble a curled-up leaf. They hang from the stems and leaves of the buck­thorn plants by a thin strand of silk. The adult but­ter­flies emerge from July to Au­gust, by which time their par­ents will have died, their life’s pur­pose, to create a new gen­er­a­tion of Brim­stones, hav­ing been ful­filled. Th­ese fresh adults feed on the nec­tar of sum­mer flow­ers through to Septem­ber, pre­fer­ring red, pur­ple and blue blooms, such as this­tles, and can also use their long pro­boscis to probe into teasels.

Win­ter shel­ter

As the tem­per­a­ture be­gins to drop, and the days get shorter to­wards the au­tumn equinox, Brim­stones seek out places to hide away for the com­ing colder months. Un­like other over­win­ter­ing but­ter­flies, which of­ten spend the sea­son in man-made out­build­ings, such as sheds, Brim­stones usu­ally pre­fer the dense ev­er­green fo­liage of holly or ivy, or a clump of bram­bles. This may be be­cause their colour and shape blends in more closely with those plants. How­ever, be­cause they will some­times emerge to feed on un­sea­son­ably warm win­ter days, Brim­stones may be seen in any month of the year. For many sum­mer but­ter­fly species, life is short at only a few weeks or a cou­ple of months at most. But the Brim­stone has an adult life­span of up to a year, mak­ing this yel­low her­ald of the spring­time among the long­est-lived of all Bri­tish but­ter­flies.

“To re­gret the ex­change of earthly plea­sures for the joys of heaven, is as if the grov­el­ling cater­pil­lar should la­ment that it must one day quit the nib­bled leaf to soar aloft and flut­ter through the air” Anne Brontë, The Ten­ant of Wild­fell Hall

A down­land flower meadow, one of many habi­tats where the wan­der­ing Brim­stone can be spot­ted. The spring blooms pro­vide an abun­dance of nec­tar, and the but­ter­flies, which are more of­ten found in the gen­er­ally warmer south­ern half of the UK, can be seen bask­ing in the gen­tle sun.

Newly-emerged adult Brim­stones spend much of their time feed­ing. They set­tle, wings closed, show­ing a pref­er­ence for pur­ple flow­ers. Their long pro­boscis al­lows them to take nec­tar that is be­yond the reach of many other species.

Two Brim­stones in flight, their veined wings il­lu­mi­nated in the April sun­shine.

The fe­male’s wings are less strik­ing but more leaf-like with a whitish-green hue.

The male Brim­stone has prim­rose-coloured fore wings, although its hind wings are lighter with a green­ish tint.

The green chrysalis is ex­tremely dif­fi­cult to pick out on a twig. Af­ter 10-14 days, the adult but­ter­fly emerges.

The cater­pil­lar finds a suit­able place to pu­pate, usu­ally a leaf or stem in low un­der­growth. It hangs it­self by tail hooks be­fore se­cur­ing it­self with a silken gir­dle.

On hatch­ing, the cater­pil­lar is a yel­lowybrown, but dur­ing the first moult be­comes green, to blend with the lush fo­liage. It hangs from the leaf by a silken thread.

A freshly-laid egg on alder buck­thorn, Fran­gula al­nus. Ini­tially, the eggs are white, turn­ing yel­low in a few days, then grey, be­fore hatch­ing into a cater­pil­lar which will feed on the fleshy leaf.

Two feed­ing Brim­stones mir­ror each other with their an­gu­lar, leaf-like wings.

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