It is spring as I write this, so I’m a bit behind with this blog entry. You may have been wondering about where all those spiders that you saw in the autumn went during the winter. Many of them came to the end of their annual life cycle and died. The species with this lifestyle have already laid their eggs; the future generation will pass the winter in an egg case.
These tiny spiderlings which emerge in the early spring are so small and inconspicuous that we hardly notice them. Other spiders that emerged from eggs laid earlier in the season may survive the winter as immatures or subadults. When they start moving around in the spring they are large enough to be noticeable.
The eggs, early-state spiderlings inside the egg case, emerged young spiders, and sometimes overwintering adult spiders often have cryoprotectant compounds in their cells and hemolymph (blood). These compounds either act like anti-freeze (lower the freezing point), or prevent the formation of large ice crystals that would damage cell membranes.
Some species of spiders may live several years and can survive the winter in a retreat or burrow. Retreats are usually silk cocoons hidden under bark, logs, rocks, or leaf litter. Very often these are near the ground where temperatures are moderate. Even under just a few inches of soil and debris, winter temperatures are much milder than above the surface. If there is a layer of snow on the ground, it can act as additional insulation from cold air. Water and ice are excellent buffers against extreme cold.
A few species can tolerate cold so well that even full-sized adults just find a nook or cranny and freeze in place. When the weather warms, they thaw and emerge.
Perhaps most remarkably, some spiders are “active” during the winter. They may take advantage of a warm winter day to wander over the snow. It isn’t clear what they are doing, but very few prey are active, so they may just be dispersing.
The most famous “winter active” spiders are the tiny denizens of the leaf litter. These animals may even molt into mature adults during the winter months. They take advantage of the relative “warmth” under layers of dead leaves and other debris on the ground. It there is snow cover, so much the better. The epigeal (soil surface) environment is actually quite hospitable to them. In Ohio deciduous forests the leaves that fell during the autumn have been decomposing by the action of fungi and bacteria. Tiny animals that feed on the decomposing leaves, or on the decomposer organisms, become quite abundant by mid-winter. Other small creatures feed on these, including many species of spiders.
Many of these winter spiders are members of the sheetweaver family (Linyphiidae). They come in a variety of sombre browns and blacks, but quite a large proportion have bright orange coloration. I’d love to know why orange is such a common color. Here is a gallery of tiny sheetweavers, none larger than 2.5mm (~1/8 inch) long. These sheetweavers often find mates and reproduce during the winter.
Some of the “larger” sheetweavers of the family Linyphiidae will emerge, build webs, and hunt as soon as the early spring weather permits. Below is an subadult male Neriene variabilis. As an adult he will be only about 4 to 4.5 mm (< 1/4 inch) total body length, but this is still twice as large as the dwarf sheetweaver spiders shown above.
In addition to the sheetweavers, there are a number of other small spiders that are active on the ground surface under leaf litter.
One last note about large spiders in winter, sometimes they do come out of hiding. When the weather is unusually nice they may show up right on the surface. Late last year I found the beautiful wolf spider, shown in the photo below, out in the tall grass next to a road while I was out “scouting” for an upcoming Christmas Bird Count. She was presumably hunting. There were other small wolf spiders in the area, great prey for a big one like this.