It always comes as a surprise to see tiny creatures moving nimbly over the surface of the snow. However, there are quite a few insects and spiders that do, thanks to the glycerol that they produce in their body fluids that keep them from freezing. The Snow Fly (Chionea sp.) is a type of wingless crane fly. Most likely its lack of wings is due to the fact that at sub-freezing temperatures it would be very hard to generate enough energy for maintaining flight muscles. They (along with other flies, mosquitoes and gnats) do have two vestigial wings called halteres, the little knobs on the fly’s thorax. They inform true flies about the rotation of their body during flight, and are thought to act as sensory organs for the flightless Snow Flies.
Throughout most of the year Snow Flies can be found in leaf litter, but come winter the adults emerge, mate and lay up to 200 eggs. The lack of predators such as dragonflies and most insect-eating birds makes winter a relatively safe time for Snow Flies to be out and about. Their life span is about two months, during which time they drink by pressing their proboscis against the snow, but they don’t eat. (Snow Fly in photograph is a female, measuring less than ½”.)
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A favorite past-time of mine is peering under logs and rocks to see what might be living there. (The logs and rocks are carefully replaced in the position in which they were found so as not to disturb the inhabitants any more than is necessary.) Recently I discovered a Crane Fly larva under a rock that was adjacent to a stream – a typical spot in which to find a soon-to-pupate larva. Roughly an inch long, the most distinguishing features are the ridges along its body, and the star-like appendages at the tip of its abdomen. If you examine the appendages closely, you will find two spiracles, through which the Crane Fly larva breathes, located in a recessed area in the center. Although you can’t see a head, it has one that is tucked into its thorax.
The Crane Fly family is the largest family of true flies, in terms of number of species. They can be found in aquatic, semi-aquatic and terrestrial habitats. True flies do not have segmented legs that they can use to hold on to the substrate when they catch their prey. Many Crane Fly larvae feed on decomposing leaves, but those species of Crane Flies which are predators are capable of forming a large knot with the muscles at the end of their abdomen. When they catch prey with their mouthparts, they enlarge the end of their abdomen and wedge the knot between stones in order to anchor themselves.