Wild Things

How one amaz­ing moth has evolved to sur­vive in the hos­tile and frigid en­vi­rons of the High Arc­tic

Canadian Wildlife - - FEATURES - By Jay In­gram

This amaz­ing moth sur­vives for years in the hos­tile and frigid en­vi­rons of the High Arc­tic

Yes, win­ter can be dif­fi­cult. But rather than de­spair about the cold and snow to come, spare a thought for Gy­naephora groen­landica, a moth that ekes out a liv­ing in the face of an ex­tra­or­di­nary col­lec­tion of win­try threats. Of­ten called the Arc­tic woolly bear moth, this in­sect ex­ists at ex­treme lat­i­tudes, up around 80 N, in Green­land and the Cana­dian Arc­tic. “Ex­ists” seems a bet­ter word than “lives,” given that it is in sus­pended an­i­ma­tion for 11-plus months of the year for six or seven years straight. Much of that time, tem­per­a­tures can be -40 C or even lower. Th­ese ex­tremes of cli­mate af­fect ev­ery stage of G. groen­landica’s life.

Let’s start with the lar­val stage pre­par­ing for its first win­ter. Each year for the next sev­eral, this cater­pil­lar, which ac­tu­ally re­sem­bles the fa­mil­iar woolly bear cater­pil­lar, will spend 11 months frozen stiff on the tundra. Ice crys­tals are an ever-present threat, but a suite of adap­ta­tions al­low it to evade death, in­clud­ing the abil­ity to su­per­cool it­self (al­low­ing its body tem­per­a­ture to fall be­low the freez­ing point of wa­ter with­out form­ing ice) while us­ing the break­down of en­ergy-gen­er­at­ing mi­to­chon­dria in its cells to man­u­fac­ture glyc­erol, an an­tifreeze mol­e­cule.

The pupa is shel­tered, if you can call it that, by wrap­ping it­self in a thin wo­ven cov­er­ing called a hi­ber­nac­u­lum, usu­ally out of the way of the pre­vail­ing wind at­tached to the side of a rock. But the slight­est per­tur­ba­tion, like the unan­tic­i­pated for­ma­tion of ice crys­tals in­side the in­sect’s cells, would be fa­tal.

It’s a mo­not­o­nous six or seven years: the cater­pil­lar emerges first thing in the spring, feeds and then, even be­fore the first day of sum­mer, re­treats back into a hi­ber­nac­u­lum un­til the next year. Even th­ese sim­ple acts are tuned for sur­vival. For in­stance, take that hi­ber­nac­u­lum on

the side of a rock, of­ten in plain sight; why isn’t it buried in veg­e­ta­tion for cover and in­su­la­tion? Be­cause sum­mer at this lat­i­tude is so brief that when spring ar­rives, a rock pro­trud­ing from the snow will warm up faster than veg­e­ta­tion or the ground, en­sur­ing that the cater­pil­lar can emerge and feed as soon as pos­si­ble.

It’s not ex­actly a feed­ing frenzy. For one thing, mov­ing around to feed in the chilly Arc­tic air causes Gy­naephora to lose heat rapidly; the “woolli­ness” of its body hairs, although help­ful, is no match for the deadly com­bi­na­tion of wind and low tem­per­a­ture. In­stead, the cater­pil­lar spends most of its time po­si­tioned per­pen­dic­u­lar to the sun, to gather as much so­lar en­ergy as pos­si­ble. But if heat is such an is­sue, why doesn’t the an­i­mal soak up the sun through July, dur­ing the com­par­a­tively warm Arc­tic sum­mer? It is the price it must pay to sur­vive its par­a­sitic en­e­mies. Both par­a­sitic wasps and par­a­sitic flies at­tack Gy­naephora, and they are of that par­tic­u­larly grue­some kind — par­a­sitoids — that lay eggs on or in the liv­ing cater­pil­lar. (This dou­bles the haz­ards of move­ment: egg-lay­ing parasites perch nearby and only land on the cater­pil­lar when it stirs.) The eggs then hatch into small lar­vae that grad­u­ally con­sume the liv­ing tis­sue sur­round­ing it, even­tu­ally break­ing through the skin of the de­ceased host.

Th­ese parasites be­come ac­tive in later June and July, but Gy­naephora shuts down be­fore then. This is an adap­ta­tion that might be keep­ing the species alive, given that 75 per cent of the lar­vae are par­a­sitized none­the­less. That early ces­sa­tion of feed­ing and the ne­ces­sity to bask rather than eat ac­count for the fact that each lar­val stage takes 11 months.

Each year it grows, then in its last year as a cater­pil­lar, things change dra­mat­i­cally. It emerges in this fi­nal spring full-size and pu­pates. Adult moths then emerge from the pu­pae, mate and lay eggs, all in a few weeks. Three en­tire life stages take only two months af­ter the ini­tial stage lasted six years.

Af­ter all this, the adults live for only a day or so: fe­males, although winged, barely move from their pu­pal co­coon. High­fly­ing males find them, they mate, and of­ten the fe­male sim­ply lays her eggs right on the co­coon that had shel­tered her, her job done. But even then, sur­vival isn’t guar­an­teed. Those eggs that in­do­lent fe­males lay on the sur­face of their co­coons are ex­posed and ob­vi­ous, and birds like snow buntings read­ily con­sume them. The eggs laid by fe­males that drag them­selves off the co­coon, or even flit­ter into the sur­round­ing veg­e­ta­tion, are some­what cam­ou­flaged and mostly es­cape pre­da­tion. Later that same sum­mer, the eggs hatch and the first tiny lar­vae pre­pare for win­ter, as the cy­cle con­tin­ues.

This is life be­yond the edge, with threats at ev­ery turn, but Gy­naephora hangs on, em­ploy­ing ev­ery sin­gle tac­tic avail­able to it. It is an im­pres­sive life.a

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