On 2 April 1986, while removing an accumulation of mosses from the roof of a covered picnic table near a home on Brookfield Road, St. John's (Fig. 1), several hundred larvae (leatherjackets) of the European crane fly, Tipula paludosa Meigen, were found overwintering in the moss between the slots of the asphalt shingles (Fig. 2). During the period 1971–1985 a heavy growth of mosses had become established in the slots between the shingles. Sufficient organic matter, together with particles of soil and sand, had accumulated in these slots to support the mosses, which gradually spread outward to the flat surfaces of the shingles (Fig. 1).

Insects are usually classified as either freeze-intolerant or freeze-tolerant (Danks 1978; Sømme 1982; Baust and Rojas 1985). Freeze-intolerant species cannot survive the formation of ice in their bodies and typically lower their supercooling points (SCP), the temperature of spontaneous ice formation, during the winter months (Sømme 1982). This is the lower lethal temperature for the insect, although prolonged exposure to temperatures above this may be harmful (Turnock et al. 1983). On the other hand, freeze-tolerant insects can survive the presence of ice crystals in their extracellular fluid and usually have nucleators that prevent supercooling below – 10°C (Zachariassen 1982).