Winter has arrived here in the Montreal area. Brrrrrr. Last night was below -25C, there’s a bitter wind, and about a foot of snow on the ground. I found my warm mitts and down jacket, but our arthropod friends don’t have this luxury! This time of year really gets me thinking about how spiders are handling the weather….
What do spiders do in the winter?
Some spiders don’t overwinter at all, and instead die at the end of the Fall, with their hardy egg cases doing the overwintering. Many other spiders, however, do remain active under the snow, in a little zone called the ‘subnivean zone‘ – between the snow and the ground. Others hunker down, nestled in leaf litter, under bark, or in otherwise concealed locations. On slightly warmer winter days, spiders can also become quite active on the snow surface. But all of this is generally not enough to guarantee survival, because even subnivean zones and hidey-holes can get very cold.
Maybe they freeze, and come back to life after it warms up? You may be inclined to think so – it certainly happens with a lot of insects. And, check out this photo that popped up on Twitter a week or so ago, by Nash Turley. It shows a fishing spider under a layer of thin ice, and it was still alive after Nash helped it out of its icy tomb. What the heck?Did this spider ‘flash freeze’, and like a good science fiction movie, pop back to life once it warmed up?
Probably not… I think ‘flash frozen’ spiders probably won’t survive. The literature generally suggests that spiders are not freeze tolerant. In other words, their tissues cannot survive the process of freezing, and ice will cause irreparable damage. Instead, I suspect Nash’s spider was already prepared or preparing for winter, and got trapped under the ice, but hadn’t yet frozen. It’s physiological adaptations involve some nifty and super-cool tricks.
Spiders are generally thought to be freeze avoidant* (e.g. here’s a paper on this), and through the process of accumulating glycols in their blood (i.e., antifreeze), are able to supercool. This means their tissues remain unfrozen at temperatures well below freezing, because they have physiologically adapted via the production of special antifreeze compounds that stops them from turning into ice. It’s a neat trick, and one that is relatively common in the invertebrate world. Of course, supercooling alone doesn’t ensure survival at extremely cold temperatures, and that’s where other adaptations come into play. Spiders will therefore find their way to the relatively insulated subnivean zone, or deep down in soil or leaf-litter. These behavioural adaptations (i.e., selecting overwintering sites), combined with supercooling superpowers, helps them get through the cold seasons.
For me, I’ll stick to my down jacket, and enjoy how Hydro Quebec helps keep our buildings warm!
* actually, we don’t know nearly enough about spiders and their overwintering physiology. I should state that I assume most spiders are freeze avoidant, based on the current literature on the topic – there’s a LOT more species to study, though!