The mammal that becomes an ice cube.
No other mammal can survive colder body temperatures than the Arctic ground squirrel. These squirrels are the cold-tolerance champions of the mammal world. Most mammals die if their body temperature drops below 70F (21C). The Arctic ground squirrel? It goes down to 27F (-2.9C) & stays alive. When August arrives, the squirrels busily eat as much as they can find, but as colder temperatures arrive, they burrow beneath the ground about 3.3 ft (1 m) deep. Temperatures stay cold there but remain steady & more predictable. Its body winds down into slow-mo, just a few breaths & heartbeats/min. Their heart rate drops from 200+ beats per minute to as low as 1-2 beats per minute, & their breathing slows to one breath every minute or two. Their brain cools to 28°F (-2°C). This is colder than the freezing point of water (32°F), yet their brain cells avoid forming ice crystals—which would normally kill tissue. Their hind limbs even fall to temperatures of 27F (-2.9C). This is the coldest recorded living mammalian tissue.
It wouldn't be hard to mistake them for being dead. For 8 months they lie there without food or water until the ground warms. Yet they wake up strong, not weak. They hibernate for 7-8 months, but inside the hibernation they cycle through hundreds of torpor bouts. Every 2-3 weeks they warm up for a few hours, which prevents muscle loss, activates their immune system, & clears waste. They live in the Arctic Circle, which encompasses Alaska, Northern Canada & Nunavut & Northeast Siberia. It's the length of time they spend in this unique state that's so extraordinary. Other hibernators (bears & bats) never reach these temperatures & don't stay cold this long. They can preserve muscle despite hibernating for 8 months by recycling proteins instead of losing muscle quickly. Humans lose muscle quickly when inactive, but squirrels constantly break down & rebuild muscle proteins during torpor/hibernation. It's like doing repairs all winter. They burned stored fat extremely slowly. This prevents muscles from being used as fuel. Their metabolism switches to "fat-only mode."
The Arctic squirrel produces cryoprotectants, which are substances like antifreeze that stabilize proteins and prevent freezing damage. Scientists are studying the Arctic ground squirrel because if we could mimic even a small part of this, we might be able to cool the body to protect heart tissue after heart attacks until surgery. For strokes, lowering brain temperature would slow cell death, buying time. Paramedics could stabilize patients by temporarily reducing metabolic demand. Cooling organs would help with organ transplants, preserving organs longer & shipping them further. And long-term metabolic slowdown could help astronauts survive extended missions. The squirrel is basically teaching us how to pause biology without breaking it.
