Spiders in Winter – they got this

Spider hunting isn’t as fun in winter because the spiders are “gone”. Where’d they go? Before yinz say they all came into the house, let me assure you, spiders have already figured this out. “Any North American spider that needed artificial shelter for the winter, would have been extinct long before Europeans arrived!” – Rob Crawford via Burke Museum blog.

Spiders have more than one strategy to survive winter or they at least have ways to guarantee the survival of their species. Most spiders overwinter in the soil, leaf litter, and under bark in various stages of their life cycles. It depends on what kind of spider it is. Spiders born in early fall (some orb weavers) literally chill in the egg sac, staying protected until spring. “Prepubescent” sub adults who were born in the summer, but haven’t yet come of age, tighten up into crevices and cracks (jumping spiders do this). Some spiders are still developing as eggs (some funnel weaving spiders). Usually, in the two cases involving eggs or spiderlings overwintering in egg sacs, the parent spiders have died by first frost. A small percentage actually stay active all winter as adults eating and reproducing (sheet web weavers and some cobweb weavers). Spiders have superpower proteins in their hemolymph (spider blood) that act like antifreeze. The spiders waiting out winter are able to handle temps as low as -4 degrees Fahrenheit (Biology of Spiders by Foelix, 3rd Ed. page 310). Below that, they stop moving and will eventually die. Pittsburgh has had some brutal winters. Minimum temperatures can go below -10 Fahrenheit about once every 5 years according to the National Weather Service, and spiders are still around; proof that they have, indeed, got this.

So which spiders are out there braving the cold? While on a recent hike (after a few subzero cold snaps), I did see “spider tracks” or draglines shining in the sun on the ends of twigs, so they’re around!

I managed to catch a tiny little spider ballooning of off a weed stalk. I have not been able to identify it. It wouldn’t stop moving for me to get a good look under the scope. What stands out most (besides being 1mm) is its high, rounded head. It could be a really tiny adult or a spiderling. Either way, it was out and about!

I captured a second spider from the bottom of a flipped log. There was no obvious web and it was small, a little over 2mm. Again, getting the spider to sit still under the scope was difficult, so guess what I did? I stuck it in the freezer for 5 minutes! It slowed her down enough for me to see that she was an adult female (fully developed epigynum or “girl parts”). I’m guessing she belongs to the sheet web family (Linyphiidae) based on eyes and body shape.

On a snowy winter day a few years ago, I was hiking Settlers Cabin Park occasionally digging around for spiders with no luck at all. Finally, underneath loose bark, I found a good sized (8mm) flat spider with long legs that seemed to fold backwards. It was from the Philodromidae family, also known as “running crab spiders”. There are 90 species in this family North of Mexico (Spiders of North America Identification Manual, 2nd Ed). They are wandering spiders and literally do run everywhere. I’ve seen them run in circles for no apparent reason. When they stop, they splay their legs out in a star shape. The second set of legs tend to be longer than the first pair which separates the running crab spiders from the regular crab spiders (Thomisidae). Philodromids overwinter as sub adults. The spider I found was an immature Philodromus vulgaris, a common species found around here. It was uncharacteristically easy to catch – too cold to run, I guess!

What happens when you bring an outdoor spider indoors?

There are spiders that are adapted to an indoor climate and can live comfortably alongside humans (see the Vacuum Evaders). Indoors is often too dry for our native spiders and, as you now know, spiders do not migrate into our homes seeking heat!

I caught an immature jumping spider in November a while back. Naturally, the immature jumping spider would hole up for the winter and emerge from its final molt ready to mate in spring. Since I kept this spider indoors, it molted into a gorgeous, colorful male…in December. Way too early for mating. Once males have had their final molt, they don’t live long. I was a little sad about it…

In conclusion, spiders are perfectly adapted to our temperate climate. If they’re native, and live outside, they follow their own cycles, the timing of which has been perfected to fall in line with the availability of prey, reproduction, and avoiding competition with other spiders. So when winter comes, you need to worry more about furnace filters and potholes that go all the way down to the trolley tracks than you do about spiders invading your home. They simply don’t have to!