January jaunts

midwinter insects brighten a cold shady hike

After a series of gray, drippy days in early January, there dawned a glorious blue-sky day. A group of hikers took advantage of it to wander up to Cropley Lake above the Eaglecrest lodge. The sun was still too low in the heavens to peek over the ridges, so we sat in the shadows to down our lunches. Most of us did so, anyhow; two of the gang peeled off to find some sun, somewhere, to warm their lunch-time.

Those of us who roosted on the shores of Cropley Lake may have lunched in the shade, but we had a fine view of several skiers swooping elegantly down from the top of Ben Stewart. Not content with climbing up Ben Stewart and having a fine ride down, the skiers then zig-zagged up a broad talus slope to the next ridgetop, to find another sweet trip down. We, being ‘of a certain age’, could only watch with stifled envy and much pleasure.

Wildlife was notably scarce on most of our little explorations, and we had to settle for very small types. We found tiny (about four millimeters long) flies that experts identified as a kind of dance fly. Unlike some kinds of dance flies, these were not forming mating swarms of ‘dancing’ flies but were all scattered around on the snow or just above it. We found one pair in the act of mating. This kind of dance fly is predatory. The larvae live in fast, cold, clean running water, hunting over and under the stones for midge and blackfly larvae. The adults prey mostly on other flies. The adults we saw could not be finding many flies at this season, so perhaps their main goal is finding mates.

Dance fly. Photo by Bob Armstrong

Near the glacier, we also found a few adult caddisflies on the snow. These might be the ones called ‘snow sedges’. Clearly, they are not the plants known as sedges, so I was curious about the name. I’m told that ‘sedge flies’ may be a name used by the British for certain kinds of caddisflies (perhaps because they are sometimes found on sedge plants), and artificial flies that mimic caddisflies are called ‘sedges’ by fly-fishers.

The caddisflies sometimes known as sedge flies have aquatic larvae that live in nifty little cases built of leaf fragments, conifer needles, or tiny pebbles. They typically forage by shredding decaying vegetation, especially leaves that have been partially decomposed by fungi. The fungi on the decaying leaves are part of the diet too, and sedge flies are fussy about the kinds of fungi they eat. Some sedge flies, including one of our local species, also graze on salmon carcasses, and many of them also collect miniscule bits of floating debris created by the shredders.

The small flies and the snow sedges are among the few adult insects that are active in winter. There are also stoneflies that leave the aquatic larval stage and fly around looking for mates in winter (see Empire 31 March, 2011). Why do these few insects emerge as flying adults in winter, when temperatures are low and snow covers most of the ground? One advantage might be that there are fewer predators, such as songbirds, spiders (although some of these roam over the snow in winter), or wasps. But what is the cost of emerging in winter?

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