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Northland Nature: Under the snow

Larry Weber For the Budgeteer News The temperature was 22 degrees, the sky was cloudy and we had a light breeze from the south as I went out on the ski trail through the woods. The route took me into a forest of mostly deciduous trees, a few pine...

Clubmoss
Clubmosses remain green under the snow among the leaf litter in the subnivean space, where the wingless winter crane fly and other insects spend the cold weather. (Larry Weber photo)

Larry Weber
For the Budgeteer News

The temperature was 22 degrees, the sky was cloudy and we had a light breeze from the south as I went out on the ski trail through the woods. The route took me into a forest of mostly deciduous trees, a few pines and along the edge of a lake.
I had skied for nearly an hour when I noticed a critter walking along the trail in front of me. I paused and took a close look at what the dark-colored one-inch-long insect was. I quickly recognized this miniature snow walker as a wingless winter crane fly.
This is an insect that I have seen dozens of times before in the snow. It walks, since it has no wings, and it was alone. I have never seen one with another of its kind or any other kind.
Wingless winter crane flies are one of several species of insects that break the rules of what we expect from insects, and reach maturity in the winter.
What I observed was one moving about on the snow’s surface, most likely in search of food and a mate, similar to what a summer insect may be seeking. They are here mostly on cloudy days of temperatures between 20 and 30 degrees.
As I skied past this wandering insect, I did not think of what it was doing out here on the snow, but what it had been doing during the last several days.
The temperature on the day I was skiing was in the 20s - the first day in nearly two weeks that we had no subzero readings, with eight of the previous ten days entirely below zero, never in the positive digits all day. Two cold snaps each lasted more than 110 consecutive hours in the negative world.
My question was not about its activity upon the snow, but about where this insect had been during the earlier cold times. For nearly the whole previous 30 days, the temperature was too cold for even this winter-adapted insect to move about. Where did it go?
The answer to this question was abundantly clear all around me: under the snow.
A few days earlier when my thermometer recorded a season-low (so far) of minus 33 degrees, I decided to check the temperature in the hidden world beneath the snow. Digging down through 15 inches of undisturbed snow, I place a thermometer.
Retrieving the device about one-half hour later, I noted that the mercury had climbed to 18 above! This was a rise of about 50 degrees.
The blanket of snow was providing a shelter for many of the local animals and plants that remain here either in the active state, as this insect was, or in a more dormant phase.
In many sites, the snowpack is beyond 15 inches and when this is added to the local leaf litter of the forest floor which also acts like an insulator, the difference in temperatures above and below the snow exceeds the reading that I noticed.
The region under the snow and on the ground is known as the subnivean layer. It is invaluable to the organisms that deal with Northland winters. The relative warmth existing here is generated by the geothermal heat of the earth, and with the leaf litter and snowpack, it is trapped here.
It is in this space of mild temperatures that mice, voles and shrews remain active.
Here, several insects, amphibians and reptiles will survive the cold in a hibernation that would fail if exposed to the cold air. Indeed, about 10 years ago, a very cold winter with little snow cover did prove to be too much for many local frogs and snakes. But with an ample snowpack now, they should come through the cold just fine.
The crane fly that I saw is not the only insect in this space. Other insects and spiders are here and may be found on the surface if the weather is mild. A thawing time of readings in the 30s can bring out hundreds of tiny snow fleas (springtails) onto the surface.
Here too are plants that are in a dormant phase as they wait for spring, and the subnivean layer is a good place to see some that are still green. Mosses, clubmosses and wintergreens keep their green leaves throughout the cold
season.
The cold will return. We will again have temperatures in the subzero range, but also rising above freezing.
And again we will see the activities of insects, spiders and others that spend the coldest days in the shelter of the subnivean space, under the snow.

Retired teacher Larry Weber is the author of several books, including “Butterflies of the North Woods,” “Spiders of the North Woods” and “Webwood.” Contact him c/o budgeteer@duluthbudgeteer.com .

Crane fly
A wingless winter crane fly walks on the surface of the snow. (Larry Weber photo)

Related Topics: WEATHERENVIRONMENT
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