Spider mites are minute arachnids, related to ticks and spiders, and are one of the most common pests affecting garden plants and indoor greenery. These tiny creatures, often barely visible, cause significant damage by piercing plant cells and sucking out the contents, leaving behind characteristic stippling or bronzing on leaves. When temperatures drop and the growing season ends, many gardeners wonder if these prolific pests simply perish. The question of whether these mites can survive the cold of winter is a major concern for anyone trying to manage their populations effectively.
Winter Survival: The Short Answer
Spider mites generally do not die off entirely when the weather turns cold, meaning winter does not provide a clean slate for gardeners. Instead of succumbing to freezing temperatures, they employ a survival strategy that allows them to bridge the gap between growing seasons. This involves a profound change in their physiology and behavior, which essentially puts their life cycle on pause. For populations living outdoors in temperate climates, entering a period of reduced metabolic activity is necessary to endure the cold and lack of host plants.
The necessity of this survival strategy changes in sheltered environments, such as heated greenhouses or homes, where conditions remain stable. In these protected microclimates, the mites can often remain active all year long, continuing to feed and reproduce, albeit at a slower rate. This continuous activity means that indoor infestations rarely experience a true rest period, unlike their outdoor counterparts.
The Overwintering Strategy: Diapause
The biological mechanism allowing spider mites to survive unfavorable outdoor conditions is called diapause, a genetically programmed state of dormancy. This is not a direct response to cold, but rather a preparatory state triggered by reliable environmental signals that announce the coming winter. The primary cue for many species, including the common two-spotted spider mite (Tetranychus urticae), is the shortening of daylight hours, or photoperiod, in late summer and early autumn. Temperature drops also play a role, reinforcing the signal to prepare for the dormant season.
For the two-spotted spider mite, the stage that enters this dormancy is the fertilized adult female, which ceases feeding and reproduction. Other species, like the European red mite (Panonychus ulmi), survive the winter as diapausing eggs, which are laid on woody tissues. The females preparing for diapause undergo a visible physical transformation, shedding their typical pale green or yellow-green color and developing a distinctly reddish-orange hue. This deep coloration is the result of accumulating keto-carotenoids, which are thought to be associated with increased stress tolerance and cold hardiness.
On a cellular level, diapausing mites experience a significant metabolic slowdown known as metabolic depression. This depression conserves energy and is accompanied by the production of cryoprotectants, such as the sugar alcohols sorbitol and mannitol. These compounds act like biological antifreeze, lowering the freezing point of the mite’s internal fluids and dramatically increasing its tolerance to cold. Once physiologically prepared, the mites migrate from the dying foliage to protected hibernation sites, such as bark crevices, leaf litter, or openings in greenhouse structures, where they remain until the favorable conditions of spring return.
Dormant Season Management and Control
Since spider mites survive the winter in protected stages, control efforts during the dormant season are particularly effective for reducing next year’s populations. Targeting these overwintering mites before they emerge in spring can significantly lower the pressure on plants during the next growing season. A foundational step is rigorous sanitation, which involves removing all plant debris, old leaves, and weeds from the garden or growing area. This action eliminates the sheltered locations where diapausing females and eggs hide.
The strategic application of horticultural oils, often called dormant oils, can also be used to smother overwintering stages. These oils work by coating and suffocating the eggs or adult females found on the bark of trees and shrubs. Application should be timed carefully to late fall or very early spring before new growth begins, ensuring thorough coverage of all potential hiding spots. Inspecting non-plant infrastructure, such as fence posts, stakes, and the edges of raised beds, is also important, as mites use these structures as hibernation sites.
For container plants or greenhouses, removing the top layer of soil or growing media can help eliminate mites that have moved down to the base of the plant or into the soil for the winter. By reducing the number of surviving individuals during this vulnerable, non-feeding stage, gardeners can prevent a rapid population explosion once warm weather and new foliage arrive. This proactive winter control is a powerful measure against the rapid reproductive cycle that characterizes spider mites during the summer months.