Too much meat to lose

Abstract

Caterpillars are getting quite numerous now on the bare spots on Cemetery Ridge. Bender saw one crawling near the tent yesterday and hastily transferred it to his mouth, remarking, “This is too much meat to lose” (Brainard DL. 1929. The Outpost of the Lost. Indianapolis, IN: Bobbs-Merrill). Thus reads the May 24th, 1884 entry in the journal of Sergeant (later Brigadier General) David Legg Brainard, a testament to the suffering and deprivation borne by the members of the ill-fated Lady Franklin Bay Expedition, a US military-led contribution to a fledgling multi-nation effort to explore the Arctic. The expedition successfully made camp in its target bay (~82°N) on Ellesmere Island on August 11th, 1881. But of the 25 men who made up the force, only six would survive, rescued in extremis from starvation at Cape Sabine (~79°N) on June 22nd, 1884, after attempts to resupply the explorers by ship had failed two years running. How ironic it must have seemed to those men, as one after another fell to cold and hunger, that the caterpillars in which Private Jacob Bender placed such desperate stock were appearing in ever greater number…and with a menacing message: if you're adapted to your environment, you can thrive; if not, it'll probably kill you. The high Arctic is not where one might expect to find a lepidopteran. But while it is true that butterflies and moths are at their most diverse in the tropics, they can be found all the way to the northernmost and southernmost temperate zones, and even well beyond. The most northerly-endemic of all is the Arctic woolly bear moth Gynaephora groenlandica, which lives right up to where Canada stops at over 83°N, and onward into northernmost Greenland (J Res Lepidoptera 1995; 34: 119–41). The caterpillars that Private Bender ate (Brainard records other possible instances) must surely have been its young. But even for this moth, life so far north is no cakewalk. It survives there only because of some remarkable adaptations. With intense cold reigning for most of the year, the window for the caterpillars to feed is short, especially when most of the day is spent basking to collect whatever energy the Sun's rays have to offer. When they first begin feeding they can increase their respiration rate by 300% within a day, but handling their energy budget properly (and avoiding deadly parasitoids) means June (or thereabouts) is all they have for grazing. Later, the decline in the quality of their plant sustenance makes it too energy-costly to digest. So they spin a hibernaculum and spend the next 11 months dormant. After the short summer is gone they face ever colder temperatures, perhaps down to –70°C, which they resist by producing glycerol and other cryoprotectant compounds that prevent damage to their cells as their bodies freeze. To encourage the biochemical pathways necessary they even break down their mitochondria, remaining essentially anaerobic until repairing the organelles when temperatures rise. Little wonder the larval stage of this insect (Figure 1) lasts seven years. An Arctic woolly bear caterpillar. I Barrio But of these solutions, Private Bender could only try to bask in the weak sunlight. Even by eating the caterpillars he found, he could not get enough food to manage his own energy balance, and at 5:45 pm on June 6th, 1884, he died – just 16 days from rescue. His succumbing to the environment, however, now serves as a warning for the entire species of G groenlandica. The Arctic is warming, and fast. Figures published in November 2016 by the Danish Meteorological Institute showed air temperatures in parts of the world beyond the 80th parallel to be some 20°C warmer than normal. How will a species so finely adapted to a life in the cold cope with such radical change? One might suppose the extra warmth could swing the energy balance a little in its favor, but some evidence already indicates that higher temperatures could cause the caterpillars’ respiration rates to overrun, reducing their growth (Oikos 2016; 125: 20–28). And what effects might a warmer climate have on their plant food, or on the parasitoids they try so hard to escape, or on the presence of predators in the place they now call home? And if G groenlandica does need the cold to survive, where will it go when there is no farther north? During that same November 2016, I saw countless spectacular butterflies as I travelled the Mekong on a slow boat through Laos, unaware they had so northerly a relative, much less one likely facing an environmental test as hard as that endured by Bender. Will it fall victim to a changing planet with no notion of what constitutes too much meat to lose? We can only hope that, like the six survivors of the expedition, the species can tough it out, and that relief comes just in time.