The snow fly – a winter-active crane fly – moves across snow at temperatures between 0 and −7°C. Conditions that would be lethal to most insects instead leave this species active, thanks to a suite of finely tuned biological adaptations.
“Rather than avoiding the cold, the snow fly actively seeks it out. It operates at the very edge of what is biologically possible,” says Marcus Stensmyr of Lund University.
In a new study with Northwestern University, researchers show the insect deploys multiple strategies at once. It produces antifreeze proteins that prevent ice crystals from damaging cells – a mechanism best known from Arctic fish. At the same time, it generates short bursts of heat, allowing it to raise its body temperature when conditions suddenly worsen.
“Heat production is extremely rare in insects. What we see here resembles mechanisms found in mammals – but in a small, cold-blooded animal,” says Stensmyr.
The snow fly is also less sensitive to cold-induced pain. A key receptor linked to cold and pain is markedly less responsive than in insects such as fruit flies or mosquitoes, enabling continued function at otherwise paralysing temperatures. To uncover these adaptations, the team became the first to map the snow fly genome at chromosomal level. The analysis revealed several unusual genes, including those linked to heat generation and antifreeze proteins.
“Evolution has produced a remarkable winter specialist that defies the limits between life and death,” says Stensmyr.
The study addresses a fundamental biological question: how small organisms without internal temperature regulation survive extreme cold. The findings may ultimately inform new ways to protect cells, tissues and materials from freezing damage.
“This is just the beginning. Nature has already solved the challenge of functioning at freezing point. That opens up new thinking in areas from medical cooling to sustainable materials for colder climates. The snow fly shows that life’s limits lie further out than we assumed,” says Stensmyr.
Alongside Northwestern University and Lund University, contributors include the NSF-Simons National Institute for Theory and Mathematics in Biology, University of Washington, ShanghaiTech University, Baylor College of Medicine, Rice University, and the Max Planck Centre for Next Generation Chemical Ecology.
The study appears in Current Biology under the title: “Coordinated molecular and physiological adaptations enable activity at sub-freezing temperatures in the snow fly Chionea alexandriana.”