Ants are ectotherms, meaning they cannot generate internal body heat and rely on the outside environment to regulate their temperature. When autumn cold arrives, the bustling summer activity slows down, triggering a complex physiological and behavioral shift across the colony. Survival through winter is not simple hibernation but a finely tuned process involving deep metabolic suppression and strategic nest relocation. This survival hinges on preparations made before the first hard freeze and the colony’s ability to enter deep dormancy to conserve energy reserves.
Entering Diapause
The most significant adaptation ants use to survive the cold is entering diapause, a state of metabolic suppression distinct from the true hibernation of mammals. Diapause is triggered by environmental cues like shorter daylight hours and falling temperatures, causing the ants’ activity levels to decrease significantly. Their movements become sluggish, and their overall energy expenditure is reduced, allowing them to survive for months on stored reserves without needing to forage for food.
To prevent cellular damage from freezing, ants engage in a process known as cold-hardening, which involves producing specialized internal chemicals called cryoprotectants. These low-molecular-weight compounds, such as glycerol or sugar alcohols, act as a biological antifreeze within their body fluids. By increasing the concentration of these solutes, the ants effectively lower the freezing point of the water inside their cells, which prevents the formation of lethal ice crystals. This biochemical transformation requires a gradual decrease in temperature over weeks, ensuring the colony is fully protected before sub-zero temperatures arrive.
Preparing the Winter Nest
To ensure a stable temperature for the entire colony, ants strategically relocate their population to a protected winter shelter, sometimes called a hibernaculum. Many species move deep underground into existing or newly excavated chambers, seeking the thermal stability of the soil. The temperature deep below the surface remains relatively constant and above freezing, even when the air above is frozen solid.
The depth of this winter retreat varies greatly by species and climate. The colony may also seek out other insulated microhabitats, such as deep within rotting logs, under large rocks, or inside the bark of trees. Worker ants often seal or narrow the nest entrances to prevent heat loss and exclude moisture, which could lead to dangerous ice formation within the tunnels.
Colony Dynamics During Winter
Once settled in the deeper, more stable nest chambers, the ant colony undergoes a collective behavioral change to conserve warmth and protect the most vulnerable members. Workers will gather tightly together in a mass, or “huddle,” using their collective body heat and mass as a form of insulation. This clustering behavior is important for maintaining a survivable temperature in the core of the nest, which houses the queen.
The colony’s reproductive activity ceases entirely during diapause, with the queen stopping egg-laying until spring. Many colonies actively reduce or eliminate the existing brood—the eggs, larvae, and pupae—before the onset of cold. This allows the colony to conserve limited food reserves by not having to feed and care for developing young that would not be able to mature until warmer weather returns. The entire colony remains in this dormant, low-metabolic state until the longer days and rising temperatures of spring signal the time for them to emerge and resume their foraging and reproductive cycles.