Spiders are cold-blooded, or ectotherms. Their body temperature is regulated by external sources and can vary with the environment without doing them any harm. When cold weather comes spiders that overwinter as adults adapt in several ways. Their metabolism slows down and they become less active. Eventually they become dormant, entering diapause, a hibernation-like state. At the same time, they start producing glycol and protein compounds which act as antifreeze and lower the temperature at which their cells will start freezing. A spider has to get to at least 23 degrees F. to freeze, and sometimes considerably lower.
Where a spider spends the winter depends in large part on the species. Some seek shelter in places where temperatures remain a little warmer than outdoors, such as in leaf litter, rock piles, building cracks and under loose bark. To help block cold wind, some will even build themselves a little pod with their silk, enclosing themselves until it is warm enough to become active again. (Photo: spider in silk pod behind loose bark)
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Some species of Northeastern spiders (including wolf and jumping spiders) overwinter as young adults and mate/lay eggs in the spring. Many spiders, however, mate in the fall, after which they lay eggs and die. Their white or tan egg sacs are a familiar sight at this time of year. One might assume that these species overwinter as eggs inside their silken sacs but this is rarely the case, as spider eggs can’t survive being frozen. Spider eggs laid in the fall hatch shortly thereafter and spend the winter as young spiders inside their egg sac.
Although egg sacs provide a degree of shelter, the newly-hatched spiderlings do have to undergo a process of “cold hardening” in the fall in order to survive the winter. On nights that go down into the 40’s and high 30’s, these young spiders start producing antifreeze compounds, which lower the temperature at which they freeze. By the time freezing temperatures occur, the spiders are equipped to deal with them throughout the winter – as spiderlings, not eggs. (Photo: Black-and-Yellow Argiope (Argiope aurantia) egg sac)