Snow flies self-amputate freezing limbs to sustain behavior at sub-zero temperatures

All living things are profoundly affected by temperature. In spite of the
thermodynamic constraints on biology, some animals have evolved to live
and move in extremely cold environments. Here, we investigate behavioral
mechanisms of cold tolerance in the snow fly (Chionea spp.), a flightless
crane fly that is active throughout the winter in boreal and alpine
environments of the northern hemisphere. Using thermal imaging, we show
that adult snow flies maintain the ability to walk down to an average body
temperature of -7 °C. At this supercooling limit, ice crystallization
occurs within the snow fly’s hemolymph and rapidly spreads throughout the
body, resulting in death. However, we discovered that snow flies
frequently survive freezing by rapidly amputating legs before ice
crystallization can spread to their vital organs. Self-amputation of
freezing limbs is a last-ditch tactic to prolong survival in frigid
conditions that few animals can endure. Understanding the extreme
physiology and behavior of snow insects is important at this moment when
the alpine ecosystems they inhabit are rapidly changing due to
anthropogenic climate change.