A mid­sum­mer’s but­ter­fly bal­let

Re­veals a fas­ci­nat­ing world of wildlife that we of­ten over­look.

BBC Wildlife Magazine - - Contents - NICK BAKER NICK N BAKER is s a nat­u­ral­ist, au­thor and TV pre­sen­ter.

Tri­an­gles of tin foil on the breeze, the but­ter­flies flash and flare, the sil­ver wash that gives them their name catch­ing both the eye and sun. This is not a ran­dom tum­bling flight: it has a pat­tern, driven by a pur­pose. It is a mid­sum­mer’s aerial bal­let, a dance of se­duc­tion and in­tox­i­cat­ing per­fume.

Among the largest Bri­tish but­ter­flies, sil­ver-washed frit­il­lar­ies are spec­tac­u­lar even on their own, while perched rel­a­tively still on a favourite bram­ble bloom. But to see a pair of them at their sex­ual peak, go­ing through the moves of se­cur­ing a fu­ture gen­er­a­tion, is some­thing to be­hold.

Sadly, this sight is today con­fined to south­ern Eng­land, in wild­flower-rich wood­land rides at the height of sum­mer. To be more spe­cific, your best chance is from around noon un­til 3pm: fe­males tend to be more ac­tive in the morn­ing and males in the af­ter­noon, with a pe­riod of over­lap be­tween the two.

The male frit­il­lar­ies pa­trol with a zig-zag flight very dif­fer­ent to their usual friv­o­lous flut­ter­ings when seek­ing the sug­ars to fuel their lust. If you see this, keep watch­ing. When a male ap­proaches a vir­gin, ripe fe­male, he casts tight cir­cles about her. Should she be up for it, she leads him on a merry dance. What now un­folds clearly has form, though it’s of­ten dif­fi­cult to work out as the hu­man eye some­times strug­gles to keep up. But in a good view, you’ll wit­ness an elab­o­rate courtship.

The fe­male but­ter­fly flies straight, drag­ging the male’s ar­dour along on an in­vis­i­ble plume of scent par­ti­cles; pheromones that she drips from glands at the tip of her ab­domen. His re­sponse is to fol­low close, al­most tail­gat­ing her ir­re­sistible odour. Next he en­gages in a loopthe-loop flight, fly­ing un­der and above her straight tra­jec­tory. Slow the ac­tion down and you would see him close his wings and stoop, an act that al­lows him to catch up, briefly over­take by a length, then rudely rise up in front of her, barg­ing into her path and caus­ing her to stall.

In that ap­par­ent clumsy, bumpy in­ter­jec­tion the male turns al­most up­side-down, with the fe­male’s an­ten­nae pur­posely close to his an­dro­co­nia, or sex brands. Com­pare the sur­face of his wings with hers and the p at­tern is clearly dif­fer­ent. He h has four stripes per forewing, w where she has none. These are his h an­dro­co­nia.

Zoom in and you’re now en nter­ing a hid­den world of mi­cro­scopic m func­tion and at tomic smell. For the mark­ings ar re more than just the reg­u­lar p ig­mented scales found on the re est of the wing – they are raised an nd tex­tured, like small brushes. Their T job is to pro­vide a large su ur­face area to dis­sem­i­nate p er­fume made by pouches at th he scales’ base. The heavy scent mol­e­cules m are wafted in her face. Se­duced by smell The T loop­ing courtship is re epeated again and again, h him show­er­ing her with the p er­fume of his in­tent, un­til she ei ither de­clines his of­fer and fl lies off, or set­tles – in which ca ase there fol­lows a more in ntimate rit­ual. There is more fl lap­ping and fan­ning, as well as s a face-to-face bow where he tr raps her be­tween his forewings an nd forces her an­ten­nae, the or rgans by which these in­sects p er­ceive pheromones, onto his an ndro­co­nial or­gans. A lengthy mat­ing m of a cou­ple of hours en nsues, a time wor­thy of the in nvest­ment of the dance.

A male does a loopthe-loop around a fe­male dur­ing their courtship flight.

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