Ants are poikilotherms, or cold-blooded organisms, meaning they cannot regulate their internal body temperature; their physiological processes are directly governed by the ambient environment. This distinction is crucial when examining cold tolerance. The artificial cold of a refrigerator, typically above the freezing point of water, triggers a temporary survival response. In contrast, the sub-zero temperatures of a freezer initiate a destructive process that few species can withstand, primarily due to severe cellular damage caused by ice formation.
Metabolic Shutdown and Torpor
When an ant is exposed to the typical temperature range of a refrigerator (34°F to 40°F or 1°C to 4°C), its body temperature drops quickly, significantly reducing its metabolic rate. This dramatic slowing causes the ant to become sluggish and eventually immobile, entering a state known as torpor.
Torpor is a temporary, reversible form of dormancy, often mistaken for death because the ant appears completely paralyzed and unresponsive. The temperature at which an ant loses all coordinated muscular function and enters this immobile state is called the Chill Coma Temperature (CCT). For many species, the CCT is well above the freezing point of water, meaning they become incapacitated long before the cold becomes lethal.
This temporary shutdown conserves the ant’s energy stores. Upon returning to warmer temperatures, the ant can typically recover its neuromuscular function and resume normal movement within minutes or hours. This survival strategy is effective for dealing with non-freezing cold stress.
The Lethal Effects of Freezing
A freezer, which maintains temperatures well below 32°F (0°C), introduces a fundamentally different and destructive challenge. For the majority of common ant species, freezing is a lethal event because they are considered freeze-intolerant insects. The primary mechanism of death is the formation of ice crystals within the ant’s body tissues.
As the temperature drops below the freezing point of the ant’s internal fluids, ice nucleation—the initial formation of a stable ice crystal—occurs. This happens at the Supercooling Point (SCP), which is the lowest temperature the insect can reach before its internal water spontaneously freezes. For most freeze-intolerant insects, the SCP is usually below the freezing point of pure water, often falling between -5°F and -22°F (-15°C and -30°C).
Once ice crystals form, they typically nucleate in the extracellular fluid, pulling water out of surrounding cells due to osmotic pressure. This movement causes cellular dehydration and shrinkage, damaging cell membranes and disrupting function. If the temperature drops too rapidly or too far below the SCP, ice can form inside the cells, which is instantaneously fatal due to the mechanical rupture of organelles and membranes.
Biological Adaptations for Cold Tolerance
While most household pest ants are freeze-intolerant, certain species, particularly those native to temperate, high-altitude, or arctic environments, have evolved specialized mechanisms to survive sub-zero temperatures. These adaptations allow some insects to lower their Supercooling Point significantly, a strategy known as freeze-avoidance.
Cryoprotectants
The most effective tools for freeze-avoidance are molecules called cryoprotectants, often sugar alcohols like glycerol or trehalose. These compounds accumulate in the ant’s body fluids, acting like biological antifreeze to depress the freezing point of water and inhibit the initial formation of ice crystals. By increasing the solute concentration, cryoprotectants allow the internal fluids to remain liquid at temperatures that would otherwise cause immediate freezing.
Antifreeze Proteins (AFPs)
Another sophisticated adaptation is the production of Antifreeze Proteins (AFPs), also known as ice-binding proteins. These proteins do not depress the freezing point as much as cryoprotectants. Instead, they physically bind to any tiny ice crystals that begin to form, preventing them from growing into large, lethal structures. AFPs create a gap between the melting point and the freezing point, a phenomenon called thermal hysteresis, which stabilizes the supercooled state and offers a powerful defense against accidental freezing.