When temperatures drop and the landscape quiets down for winter, many assume that spiders, being cold-blooded creatures, simply perish from the cold. The truth is that the vast majority of spiders in temperate regions do not die off. Instead, they employ a complex suite of behavioral and physiological strategies to survive the harshest months of the year. The arachnids you see weaving webs in the spring are often the same individuals, or their young, that successfully navigated the winter season.
Clarifying Winter Dormancy
Spiders do not undergo the same deep, regulated sleep seen in mammals, which is called true hibernation. Instead, they enter specialized states of reduced activity known collectively as dormancy.
One form is diapause, a programmed, hormonally controlled suspension of development and metabolic rate. This state is anticipatory, triggered by environmental cues like shortening daylight hours, preparing the spider for the cold long before temperatures become lethal. The other type of dormancy is quiescence, a more immediate response where activity and metabolism slow down in direct proportion to the chill. Unlike diapause, quiescence is instantly reversible; the spider will become active again the moment conditions improve. Both mechanisms ensure the spider conserves energy and limits exposure to freezing temperatures by minimizing movement and biological function.
Internal Physiological Adaptations
To survive temperatures below freezing, spiders rely on a biochemical strategy known as cold hardening. This process involves the production of natural antifreeze compounds called cryoprotectants, which are synthesized within the spider’s body fluids as a response to falling autumn temperatures. The most common of these is glycerol, a sugar alcohol that functions similarly to the antifreeze used in car engines.
Glycerol works by increasing the concentration of solutes in the spider’s hemolymph, or blood, which effectively lowers the freezing point of the body fluids. This allows the spider to enter a state of supercooling, where its internal temperature drops below zero degrees Celsius without ice crystals forming. Some species also produce specialized proteins, known as thermal-hysteresis factors, which further depress the freezing point and help inhibit the growth of any ice crystals. These internal adaptations protect the spider from the cellular damage caused by ice formation, which would otherwise be fatal.
Overwintering Locations and Shelter
Internal chemistry alone is not enough, so spiders combine their physiological adaptations with a behavioral strategy: seeking out stable, insulated microclimates. Their primary defense is finding locations where the temperature remains consistently above their lethal limit. Outdoor spiders often burrow deep into the leaf litter on the forest floor, a material that provides excellent insulation.
They also seek refuge beneath loose bark on trees, inside rock crevices, or within the abandoned tunnels of other animals. Snow cover, when present, acts as an effective blanket, creating a stable, warmer layer of air near the ground. Many common house spiders move into human structures, finding stable temperatures in basements, sheds, and wall voids, which serve as accidental, year-round shelters. Some smaller species weave a dense, silken retreat or pod around themselves in a sheltered spot, further insulating their bodies.
Life Stage Variations in Winter Survival
The stage of life a spider is in when winter arrives dictates its specific survival strategy. Some species, such as certain wolf spiders, overwinter as young adults and rely on their full physiological cold-hardening capabilities. In contrast, many orb-weavers and garden spiders complete their life cycle in the fall, with the adult female dying after laying her final egg sac.
In these cases, the winter survival of the species rests entirely on the silken egg sac. These sacs are laid in a protected location and often contain dozens to hundreds of eggs. For species that lay eggs in the fall, the eggs frequently hatch quickly into tiny spiderlings. These juveniles spend the entire winter huddled inside the insulating silk sac, undergoing their own cold-hardening process and producing cryoprotectants until the warmth of spring triggers their emergence.