|NIKI WILSON – On Science, Jasper Fitzhugh|
|March 14, 2013|
Recently, a fellow insect enthusiast (that’s you Sue Young-Leslie) sent me a message asking about “those winter spiders” she’s been seeing around. You know the ones, most frequently seen dragging their sluggish, segmented rears across the snow pack on warm winter days.
I’m not afraid to admit that bug identification makes my toes tingle, so naturally I dropped everything to find out what it was. After photo confirmation, we decided Sue was talking about the wingless winter cousin of the summer cranefly, ingeniously called the snow cranefly. It’s easy to mistake these guys for spiders, given the way they creep along.
Around here they’re usually dark-coloured (to attract heat), with six long, spindly legs, and an ovoid, segmented body about 3–10 mm long. Sometimes they’ve got a nasty, upturned spike on their rear, but don’t worry, this is for laying eggs and not stinging humans.
Although they have not been studied intensively, the thinking is that snow craneflies live in the burrows of ground squirrels and other small mammals. This keeps them warm, and also offers them a food source; they feed off the fleas, mites and other small goodies that live on the rodents. Everyone has to eat, right?
Adults disperse from the burrows in the autumn/early winter to mate. After a few weeks of mating, the males kick the bucket, and the females go back under the snow to lay eggs in the soil, using that pointy ovipositor on their back end. Then, until April or so, you’ll see them creeping around, having reached the surface of the snowpack by climbing up logs, trees and shrubs.
Snow craneflies aren’t the only bugs that make a go of it in the winter. Sometimes they are confused with the snow scorpion fly, although it is generally much smaller, and has much shorter legs. Scorpion flies have a long head and a pronounced, down-turned beak. Don’t forget your magnifying glass if you want to get a really good look. The good news is they’re not moving too fast, so you’ve got time to closely inspect them.
Other small critters that make it work in the cold include snow worms, spring tails, small winter stoneflies, and a primitive order of “ice insects” that are related to earwigs. According to Ben Gadd in the Handbook of the Canadian Rockies, these ice insects can’t tolerate temperatures greater than eight degrees Celsius — place one in your hand and it will die.
For most winter insects, avoiding freezing and staying warm enough to move are major challenges. Insects are ectotherms, meaning they rely on external forces to produce their heat. That is why most are equipped with adaptions that prevent their bodies from freezing. This is super cool stuff.
And by super cool, I actually mean super-cooling stuff. Many freeze-avoiding winter insects supercool their bodily fluids to avoid the formation of ice crystals — crystals that would rupture cells and eventually kill their host. How do they do this?
In order for a liquid like water to freeze, it needs a particle, like dust, to act as a nucleus around which the ice crystal is formed. This is called, not surprisingly, the ice-nucleating-agent, or INA. Some insects are able to remove INA’s from their bodies as they prepare for winter, thereby allowing the fluid in their body to remain in a liquid form, albeit really, really cold.
Super-cooling is further enhanced when bugs produce anti-freeze compounds called cryoprotectants. These reduce the lethal freezing temperatures in their bodies. Ethylene glycol, the same compound found in antifreeze for cars, is the most common cryoprotectant.
Cryoprotectants are usually distributed uniformly throughout the bug’s body. The lower the temperature, the more viscous the body fluids become. This helps ward off the freezing, but makes movement tricky. So when you see snow craneflies drunkenly stumbling across the snow, give them a break for goodness sake. You try walking with super-cooled liquid in your limbs and see how far you get.
Now you know a bit about snow craneflies, complete with bonus material about insect winter survival techniques. A big thank-you to Sue, and the other folks who stop me on the street and shoot me messages to share stories and ask, “What is this?” Talking to you about critters, plants and fossils makes writing this column worthwhile. In fact, it’s my favourite part.