The Cold-Loving Snowfly

Posted By Wolf Ridge Naturalist
February 2, 2015


Over the last few weeks I’ve been occasionally surprised by the sight of tiny, arachnid-like creatures ambling across trails, dark and clear against the white snow. Upon closer inspection, these beings, though having their legs raised above their bodies spider-style, turn out to be true insects of some sort. They are wingless craneflies of the genus Chionea: flightless relatives of the bumbling, long-legged mosquito-like flies sometimes known as Daddy Long-Legs in Europe. Here in the Midwest, these cold-loving insects are often called snowflies. But why are they out prowling the snowy wastes at a time of year when most insects are overwintering as an egg or pupa?

The answer lies with predation. The niche of the wingless cranefly involves being active during the winter in order to miss out on visits from the many summer animals that would otherwise snack on them. There are no ants about; nor are there amphibians or spiders – and even the birds (most of them, as least) have flown south. The winter environment is a safe one for the snowfly.

Being abroad in frigid temperatures requires an ectotherm (what used to be called “cold-blooded”) to have special adaptations. As adults, these craneflies never feed, having already gained all the nutrients they’ll ever need as larvae. This is useful to the adults as their bodies don’t contain food particles that could potentially grow into ice crystals, rupturing their cells. They also have electrolytes in their haemolymph (insect “blood”, essentially) that lower the freezing point of this liquid, allowing them to be active in temperatures as long as -6 C (21.2 C). It’s something like a natural antifreeze. Finally, these flies mostly inhabit an area just below the most recently-fallen snow where heat is conserved and clear, warm areas open up between the earth and the topsnow. This zone is known as the subnivean environment, and its use by these craneflies shows that behavioural adaptations are as important as physical ones.

So keep your eyes open on the trail for snowflies, and be reminded how nature has a myriad ways in which to respond to the changing conditions and seasons.

– Cian Gill