Spiders are ectotherms, meaning they cannot regulate their body temperature internally like mammals or birds. Their body temperature is directly dependent on the ambient temperature of their surroundings. This physiological reality dictates that every aspect of a spider’s life—from movement and hunting to digestion and reproduction—is intrinsically tied to the warmth or cold of its environment. When temperatures drop, their metabolism slows down, making them sluggish. If temperatures climb too high, they risk cellular damage and water loss. Spiders have developed behavioral and physiological adaptations to function across a wide thermal spectrum, seeking a specific thermal “sweet spot” required for optimal function.
Optimal Temperature Range for Activity
Spiders require a specific thermal range to maintain peak metabolic activity, allowing them to hunt most effectively and reproduce successfully. This optimal temperature range varies widely between species, reflecting the diverse microclimates they inhabit. For example, the European garden spider, Araneus diadematus, selects a mean preferred temperature around 22.5°C (72.5°F), while the giant house spider, Eratigena atrica, prefers a significantly cooler temperature around 13.7°C (56.7°F).
When temperatures fall below this optimal window, the spider’s metabolism slows, resulting in reduced activity. Conversely, if the temperature rises slightly above their preferred range, the metabolic cost of movement can become too high, leading to thermal stress. This thermal dependency means a spider’s ability to locate prey, escape predators, and successfully mate is directly correlated with maintaining a suitable operating temperature. Many spiders engage in behavioral actions, such as basking in the sun to absorb heat through their exoskeletons, to reach their preferred temperature and increase activity levels.
Survival Mechanisms in Cold Conditions
To survive winter or periods of extreme cold, spiders utilize two primary biological strategies: diapause and cryoprotection. Diapause is a state of metabolic suppression similar to hibernation, where the spider dramatically reduces its energy expenditure and activity. This physiological shutdown can reduce the metabolic rate to less than 10% of the summer activity level, conserving energy when both temperatures and food resources are scarce.
Many cold-tolerant spiders also produce natural “antifreeze” compounds called cryoprotectants. These are typically sugars and sugar alcohols, such as glycerol and sorbitol, which accumulate in the spider’s hemolymph (the equivalent of blood). The presence of these substances prevents the formation of damaging ice crystals within the tissues, effectively lowering the freezing point of their body fluids. This mechanism allows some Arctic species to survive in a supercooled state at temperatures far below 0°C.
Behaviorally, spiders seek out stable microclimates that offer protection from the deepest cold, often entering sheltered areas under bark, stones, leaf litter, or deep crevices. These locations act as non-freezing buffers against the surrounding environment. Juvenile spiders of some species may also overwinter within their egg sacs, which provide an insulated envelope until spring.
Handling Extreme Heat and Desiccation
When temperatures rise significantly above their optimal range, the greatest threat to a spider is desiccation, the rapid loss of body water. Spiders have a high surface-area-to-volume ratio, making them particularly vulnerable to dehydration in hot, dry conditions. This susceptibility forces them to rely heavily on behavioral thermoregulation to find relief.
Behavioral responses to heat include actively seeking shade, retreating into burrows or cool, moist soil, and moving to the underside of objects to escape direct solar radiation. For example, wolf spiders that live in burrows retreat deeper inside when the surface temperature is too high, often limiting surface activity to cooler parts of the day. This search for stable, cooler microclimates is why spiders may be found indoors during extreme summer heatwaves, as a house provides a consistent, lower temperature and often higher humidity than the outdoor environment.
The physiological limits for heat tolerance are species-specific and can be surprisingly high, though exposure time is a significant factor. Some social spiders have a critical thermal maximum (CTmax)—the temperature at which motor function fails—of nearly 49°C (120.2°F). This high tolerance is often coupled with an immediate behavioral escape response at a lower temperature. Less mobile species, such as sedentary web-building females, are more vulnerable to heat stress because they are limited in their ability to quickly move to cooler spots, which can lead to mortality if the heat persists.