Spiders often disappear as cold weather arrives, leading many to assume they enter true hibernation, similar to bears. This is inaccurate because spiders lack the complex physiological mechanisms necessary for mammalian hibernation, which involves regulated body temperature and deep torpor. As cold-blooded organisms, spiders cannot generate internal heat, meaning their body temperature depends directly on the surrounding environment. Instead of true hibernation, spiders employ a survival strategy known more accurately as “overwintering” or “dormancy” to persist through the harsh conditions of the cold season. This process involves a shift in metabolism and behavior to conserve energy and avoid freezing until warmer temperatures return.
The Scientific Reality of Spider Dormancy
The specialized state that most spiders enter to survive winter is a form of physiological dormancy called diapause. Diapause is a genetically programmed response that arrests development and suppresses metabolic activity, allowing arthropods to wait out predictable environmental stress. Initiation is typically triggered not solely by temperature, but by earlier signals like the shortening of daylight hours, known as the photoperiod.
As the days grow shorter in late summer and early autumn, spiders receive the cue to begin preparations for the coming cold, well before the first frost. This programmed slowdown is distinct from simple quiescence, which is a temporary inactivity caused by immediate cold that is instantly reversible with warmth. Diapause, by contrast, is a deeper state that requires specific internal and external conditions to be terminated, ensuring the spider does not emerge too early during a brief winter warm spell.
The spider’s life stage dictates how it uses dormancy to survive. Some species overwinter as adults, others as juveniles, or remain protected within an egg sac. For many larger, short-lived species like annual orb weavers, the adult dies after mating, and only the dormant egg sac survives until spring hatching. The adult spiders that do overwinter become significantly less active, conserving the limited energy reserves they have stored from the warmer months.
Surviving Sub-Zero Temperatures
To survive cold climates, spiders must prevent internal water from freezing, which causes lethal tissue damage from sharp ice crystals. Spiders that overwinter in exposed locations or microclimates that occasionally dip below freezing have evolved a remarkable internal defense mechanism: the production of low-molecular-weight compounds known as cryoprotectants.
These compounds, which often include sugar alcohols like glycerol, act as a biological antifreeze within the spider’s hemolymph, or blood. Glycerol increases the concentration of solutes in body fluids, lowering the freezing point through supercooling. By depressing the temperature where ice spontaneously forms, the spider remains in a supercooled, liquid state even when ambient temperatures drop below zero.
Accumulating these cryoprotectants is part of a metabolic shift called cold-hardening, activated by decreasing temperatures and photoperiod. In some species, specialized proteins (thermal-hysteresis factors) are produced alongside glycerol. These proteins prevent accidental ice crystals from growing and spreading, providing extra protection against freezing. This chemical strategy allows many spiders to survive temperatures that would instantly kill organisms without such safeguards.
Common Overwintering Locations
To maximize their survival chances, spiders seek specific microclimates offering insulation and stability, minimizing exposure to the most extreme temperature fluctuations. Most spiders remain outdoors, utilizing natural shelters that provide a protective buffer against the elements. A common location is the subnivean zone: the insulated space beneath a layer of snow and the topsoil or leaf litter.
Other outdoor locations include:
- Deep crevices in tree bark.
- Under loose stones.
- Dense piles of decaying leaf litter, where organic material breakdown generates subtle warmth.
- Outbuildings like woodpiles, sheds, or garages, which offer dry, undisturbed spaces.
These sites offer a stable temperature consistently above the lethal freezing point.
While many spiders overwinter outdoors, some species adapted to human dwellings seek refuge inside homes. Spiders that enter a house during the fall typically hide in quiet, undisturbed areas like basements, attics, crawlspaces, or within the voids of walls and foundations. In the stable, warmer environment of a heated home, these spiders may not enter deep diapause and can remain somewhat active throughout the winter, occasionally emerging to hunt or find water.