Nick Baker’s Hid­den Bri­tain

BBC Wildlife Magazine - - Contents - NICK BAKER Re­veals a fas­ci­nat­ing world of wildlife that we of­ten over­look. NICK BAKER is a nat­u­ral­ist, au­thor and TV pre­sen­ter.

A chance en­counter with a snow flea

There I was, in De­cem­ber – I had pulled over in a patch of heathy wood­land to an­swer a call of na­ture when I caught sight of move­ment on the ground by my feet. It was win­ter – what could it be?

On closer in­spec­tion, I re­alised I had found my first (and, to date, only) snow fleas, Boreus hye­malis. The frigid win­ter months are not known for en­to­mo­log­i­cal ex­u­ber­ance. Wings are a ‘no-no’, un­less you’re the tough­est of midges or moths. That’s prob­a­bly why the snow flea, one of our most bizarre in­sects, is wing­less.

De­spite its name, it isn’t a flea or a fly. It be­longs to the scor­pion flies, a group of in­sects, mostly denizens of sum­mer hedgerows. Bri­tain has three other species of scor­pion fly, all be­decked with pic­ture-frame wings. The males pos­sess a cu­ri­ous swollen gen­i­tal cap­sule, which is held at the tip of their slim ab­domen and curls back­wards, pro­duc­ing a threat­en­ing look, rem­i­nis­cent of a scor­pion’s tail.

The snow flea lacks pretty wings or out­wardly dis­tinc­tive gen­i­tals. But it has the other di­ag­nos­tic fea­ture of this fam­ily of in­sects – a long ‘face’. In re­al­ity, this is an elon­gated ros­trum, or beak, with mouth­parts at the tip.

A fly that can’t fly sounds like an oxy­moron. Yet it doesn’t stop the snow flea get­ting about, which it does by walk­ing or by jump­ing up to 5cm in a sin­gle bound. Though it has no ob­vi­ous ex­ter­nal adap­ta­tions for the salta­to­rial task of leap­ing, the snow flea does have long legs and the use of an elas­tic pro­tein called re­silin. This acts like an in­ter­nal cat­a­pult and is the same stuff that gives ac­tual fleas their bounce – to­gether with snow fleas’ small size (around 5mm), it ex­plains at least part of the com­mon name.

The rest of the moniker prob­a­bly refers to the fact that the species is usu­ally no­ticed against snow. These in­sects live mainly in mossy sub­nivean (be­low the snow) habi­tats, oc­ca­sion­ally gath­er­ing on the sur­face. They don’t need snow but they do best in re­gions with harsh win­ters.

As in­sects, they are ec­tother­mic (cold-blooded), so can­not gen­er­ate body heat. Rather than be at the mercy of the cold and its cell-rup­tur­ing ice crystals, they have the abil­ity to su­per­cool. They lower the freez­ing point of fluids in their cells, us­ing spe­cial pro­teins and poly­hy­dric al­co­hols, so that ice crystals don’t form. Be­ing ac­tive in cold con­di­tions is worth it – there is less risk of meet­ing preda­tory in­sects.

Win­ter ro­mance

The pair I had dis­turbed were pretty much the only things mov­ing in the frozen land­scape, so got my full at­ten­tion, but I no­ticed some­thing odd. The fe­male – eas­ily recog­nised by her long ovipos­i­tor (egg-lay­ing tube), which gives her ab­domen a sharp point – was on the back of the male.

It’s not strictly true that male snow fleas have no wings – they are re­duced to strange, spine-like pro­jec­tions – and this male was busy us­ing his like a large pair of sex­ual tongs. He had ro­tated them be­hind his tho­rax, and clamped them about the head cap­sule of the fe­male, hold­ing her in po­si­tion for mat­ing.

These amaz­ing lit­tle in­sects are an en­to­mo­log­i­cal high­light of win­ter, for those de­ter­mined enough to look.

Snow fleas have a fairly wide­spread dis­tri­bu­tion across the UK– only the south-west seems to miss out.

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