Ants, like all insects, are poikilotherms, meaning their internal body temperature is directly dependent on the external environment. This biological reality makes the cold temperatures of winter a survival challenge for an ant colony in temperate climates. Their movements become sluggish and their metabolism slows dramatically as air temperature drops. The entire colony must rely on coordinated behavioral adjustments and physiological changes to successfully endure the freezing months until spring returns.
Preparing the Colony for Cold Weather
The ant colony begins its winter preparations with behavioral and structural modifications as autumn temperatures start to fall. Worker ants stop their foraging trips, as surface food sources become scarce and the above-ground environment is too cold for sustained activity. The focus shifts to consolidating the colony’s resources and sealing the nest against the impending cold.
Workers actively close off many of the nest’s peripheral tunnels and entrances with soil and debris to reduce drafts and conserve moisture and heat within the main chambers. This structural sealing helps to stabilize the microclimate deep inside the colony. Many species spend the preceding warmer months consuming food to build up substantial fat reserves, which will sustain them during the long period of dormancy. Some harvester ant species collect and store seeds in underground granaries, while others, like honeypot ants, designate workers to gorge on sugary liquids, turning them into living storage vessels to feed the colony when resources are inaccessible.
The Winter Retreat: Deep Underground
The colony’s primary survival strategy relies on seeking a location where temperatures remain stable and above freezing. As surface temperatures plummet, the colony, including the queen and the brood, migrates to the deepest parts of the nest, often well below the frost line. This descent is crucial because the surrounding soil serves as an insulator, buffering the chambers from the extreme temperature swings occurring at the surface.
The constant temperature of the earth a few feet down provides a warm sanctuary, sometimes even benefiting from geothermal heat. Once situated, the ants engage in a collective warming behavior by forming a cluster around the queen and any remaining larvae. This huddling conserves the heat generated by the ants’ collective metabolic activity, ensuring the survival of the queen, which is the lifeline of the colony. The stability of the underground environment protects the colony from fatal ice crystal formation.
Entering Diapause and Physiological Changes
The survival mechanism is diapause, a metabolically arrested state distinct from simple hibernation. Diapause is triggered by environmental cues, such as shortened daylight hours and temperature drops, and involves a reduction in the ant’s metabolic rate. This slowdown conserves the colony’s energy stores, allowing them to subsist on the fat reserves accumulated in the autumn.
To prevent cellular damage from the cold, adult ants and some larvae undergo cold hardening by producing specialized molecules called cryoprotectants. The most common of these is glycerol, a sugar alcohol that acts as a biological antifreeze. Glycerol is synthesized and circulated throughout the insect’s body fluids, significantly lowering the freezing point of the hemolymph. The accumulation of glycerol prevents the formation of damaging ice crystals inside the ant’s cells. In some species, up to ten percent of the ant’s body weight can consist of glycerol during the winter months.
Other cryoprotectants, such as the amino acid proline or the sugar trehalose, may also be produced. This biochemical adaptation allows the individual ants to survive temperatures that would be fatal without such protection.