Science of Winter: Why are there tiny insects in the snow?
This winter, Postmedia’s Tom Spears looks at what makes our coldest season tick. It’s a series we call The Science of Winter, and today we grab a magnifying glass to find out why those tiny black dots on top of the snow are moving. Yup, even snow has bugs.
Winter, the insect-free season, is nothing of the kind.
It was the end of November when biologist Michael Runtz went to Algonquin Park to find an eagle, a few otters on a partly-frozen lake, a lot of animal tracks in the snow — and a lot of “tiny dark objects moving slowly across the snow.”
A closer look revealed several types of spiders, two species of tiny flies, two types of wingless snow flies and a bunch of wingless creatures about five millimetres long called snow scorpions, which he had never seen before.
Especially on mild winter days, the snow comes alive with mysterious insects. You just have to look, says Runtz, who teaches at Carleton University.
Ontario has a couple of species each of snow scorpions (named solely for their shape) and snow flies, and one main type of snow flea, also called a springtail. Add a handful of fungus gnat species, and that’s about the full set of snow insects.
“They actually live on the ground, but they come up on the snow, often to reproduce,” Runtz said. “In the case of snow fleas, though, they’re coming up to feed on algae on the snow, or spores of mosses perhaps. The snow scorpions mate on top of the snow.
“On warm days in winter, especially near that freezing point threshold, then you start to see these little fellows on top.”
It’s thought that many crawl up to the surface at the base of a tree, where warmth often creates an opening in the snowpack.
“Snow fleas especially are abundant in late winter. March is a big month for them. Sometimes you can go out and see the snow literally black with billions and trillions of these creatures. The population size is unbelievable.”
These insects stay active under the snow all winter, protected from freezing by internal antifreeze proteins and by a layer of insulating snow. Winter keeps them warm.
“You often see small spiders crawling around on the snow on warmer days. Why are they there? Are they coming up because they can, or is it getting wet under the snow? There are a lot of mysteries about these.”
Mostly the species prefer forest settings.
Some have odd body parts. Snow fleas, also known as springtails, “have an appendage on the underside that allows them to spring up in the air and move many times their body length very quickly,” Runtz said.
“Snow scorpions can jump too. They’re pole-vaulters, almost.
“These things are tiny and they’re really common. It just means looking down at your feet as you ski or snowshoe through snowy terrain when the temperature is right. You tend to find them more in forest openings.
“There’s still a lot of mystery. You can imagine how hard it is to study these little guys. It’s next to impossible.”
Recently Runtz watched a pileated woodpecker chopping into a white pine in search of dormant carpenter ants. “When I took a closer look, I noticed black, pepper-grain-sized material adorning the perimeter of each hole where sap had been oozing,” he wrote in an article.
The dots were snow fleas/springtails.
“Initially I wondered if the tiny animals – 1.5 mm long – were eating sap. Snow fleas mysteriously appear atop snow in late winter in incalculable numbers. It is unknown why they do or where they come from but from the soil is suspected. Their diet includes fungal spores, algae, bacteria, and sap.
“But close-up views revealed that these insects were actually mired in the sap. Some were barely alive, weakly moving legs or antennae in a vain attempt to escape. If they did come to eat the sap, their meal had become a death trap.”
None of these bugs of winter will bite you. You’re safe from mosquitoes and black flies. For now.