Spiders are ectotherms, meaning they cannot internally regulate their body temperature. Their survival depends entirely on external conditions as temperatures drop. Spiders must actively avoid freezing, as ice crystal formation inside their bodies is fatal. To survive the cold months, they employ a combination of physiological adaptations and behavioral choices. Strategies range from producing biological antifreeze to seeking insulated microhabitats.
Physiological Survival Mechanisms
Many spiders prepare for cold weather by undergoing a process called diapause, a state of metabolic slowdown analogous to hibernation. This dormancy is triggered by environmental cues like shortening day length and cooling temperatures. Diapause significantly reduces the spider’s need for food and energy during the winter. The metabolism of a spider in diapause can drop to less than 10% of its active summer rate, allowing it to survive for extended periods without foraging.
To prevent their internal fluids from freezing, spiders produce specialized chemicals known as cryoprotectants. These are often glycerol or other sugar alcohols that function as biological antifreeze, lowering the freezing point of the spider’s hemolymph, or blood. This biochemical adaptation, often called supercooling, allows some species to survive temperatures as low as -4 degrees Fahrenheit without ice forming in their tissues. The production of these compounds increases gradually as winter approaches, a response that is crucial for cold tolerance.
Outdoor Shelters and Hibernation
The majority of spider species that overwinter as adults survive by seeking out highly insulated microhabitats outdoors. They search for locations that offer thermal stability, which shields them from the extreme temperature fluctuations of the air. These natural shelters are primarily found close to the ground, where the insulating effects of snow and earth are most pronounced.
A common winter location is under the loose bark of trees, which provides a tight, dry space shielded from wind and precipitation. Spiders also burrow deep into leaf litter and the topsoil layer, where decomposing organic material provides a slight increase in temperature. Other species utilize the subnivean zone, the insulated space between the ground and the snowpack. This allows them to remain active or semi-active while protected from harsh air temperatures. Some spiders seal themselves within abandoned insect tunnels, rock crevices, or self-spun silk retreats.
Indoor Spiders and Egg Sac Strategy
Spiders that live entirely in human structures, known as synanthropic species, do not need the same cold-weather adaptations as outdoor spiders. House spiders, such as the common American House Spider (Parasteatoda tepidariorum), remain active year-round in stable environments like basements, attics, and wall voids. Although their activity may slow down in unheated spaces, they do not enter a deep diapause state. This is because they are generally not exposed to freezing conditions.
A different strategy is employed by many annual species, such as orb weavers, whose adult life cycle concludes in the late autumn. The adult spider dies with the first hard frost, and the species survives entirely in the egg stage. The female lays eggs inside a durable, heavily protected silk egg sac. This sac is then concealed in a sheltered location like under eaves, in vegetation, or within wood piles.
The spiderlings often hatch within the sac before winter. They remain protected inside the sac until the warmer temperatures of spring arrive. Spring signals the time for them to emerge and disperse.