Eight animals that cheat the killing cold

In the freezing Southern Ocean the crocodile icefish is the only vertebrate on Earth with no red blood cells and no haemoglobin; its blood runs as colourless as water. It absorbs oxygen straight from the frigid, oxygen-rich sea through huge gills and bare, scaleless skin, and fills its veins with antifreeze proteins that grip onto tiny ice crystals and stop them from ever growing larger.

Hibernating through an eight-month Arctic winter, the ground squirrel lets its core drop to about minus 2.9 degrees Celsius, nearly three degrees below freezing and the lowest body temperature ever recorded in a mammal. Its blood stays liquid by supercooling, because it scrubs out the tiny specks that ice would crystallise around. Every few weeks it shivers itself warm again for a day, then sinks back below zero.

Sealed under the ice of an oxygen-starved pond, the crucian carp does what would kill almost any other animal: it keeps living for months with no air at all. Rather than let deadly lactic acid pile up, it converts the waste into ethanol and breathes the alcohol out through its gills. By late winter its blood can run above the drink-drive limit, the only fish that gets through the freeze by getting tipsy.

Painted turtles hatch in late summer but stay underground in the nest all winter, often supercooled below freezing without turning to ice. Buried where almost no air reaches, the hatchlings go months without oxygen and hold off the acid that builds up by dissolving minerals from their own shell and bones to neutralise it. When spring finally warms the soil, the tiny survivors dig their way up to the surface.

The Siberian salamander endures cold no other four-legged animal can, surviving freezing down to around minus 45 degrees Celsius by pumping its cells full of glycerol antifreeze. Animals dug out of the permafrost have thawed and crawled off after years locked in the frozen ground, with one disputed account claiming decades. When the ice finally lets go, the little salamander simply ambles away.

When a Southern pond freezes over, alligators do not flee. They sense the ice forming and hold their snouts up through the surface so the water locks around them with only their nostrils left clear. Stuck like that in a deep cold sleep called brumation, their hearts slowing to just a few beats a minute, they keep breathing through the ice for days until the thaw finally sets them loose.

In water barely above freezing the Greenland shark may live more than 400 years, the longest-lived vertebrate known. Its flesh is steeped in a compound called TMAO, a natural antifreeze that keeps its proteins working in the cold and the deep, and that also makes the meat poisonous to eat fresh, fit for food only after months of fermenting. It grows about a centimetre a year and ages in no hurry at all.