The Nine-banded armadillo (Dasypus novemcinctus) is the only armadillo species found across the southern and southeastern United States, a range that has been expanding northward. This mammal is recognizable by the bony, protective plates covering its body. Armadillos do not hibernate; they lack the biological machinery for the deep, sustained metabolic shutdown of true hibernation. They must employ other methods to endure cold periods.
The Difference Between Hibernation and Torpor
Hibernation and torpor are both states of metabolic suppression, but they differ significantly in depth and duration. True hibernation is a long-term, highly regulated process lasting weeks or months. During this state, an animal’s core body temperature drops dramatically, and its metabolic rate slows to one to two percent of its active rate. This deep dormancy requires massive reserves of stored body fat to fuel the inactivity and the expensive process of arousal.
Torpor, by contrast, is a short-term, reversible state, often lasting only a few hours, usually overnight. The drop in body temperature and metabolic rate is much shallower, with the metabolic rate decreasing only to about 30 percent of the basal rate. Torpor is triggered by immediate environmental pressures, such as a temporary drop in temperature or lack of food. Animals can wake up relatively quickly to forage or escape danger.
Armadillo Physiology and Cold Tolerance
The nine-banded armadillo’s physiology prevents it from achieving true hibernation. Unlike dedicated hibernators, armadillos do not accumulate the massive fat deposits necessary for sustained dormancy and arousal. They lack Brown Adipose Tissue (BAT), which produces heat through non-shivering thermogenesis, severely limiting their ability to generate internal heat.
Armadillos possess a relatively low basal metabolic rate compared to other mammals, making it challenging to generate sufficient body heat to withstand prolonged cold. Their dermal armor provides protection but offers very little insulating value against environmental cold. Furthermore, sparse hair provides almost no thermal barrier, making them highly sensitive to sustained low temperatures.
Their poor thermoregulation means they struggle to maintain a stable core temperature when ambient temperatures drop near or below freezing. Studies suggest an adult armadillo cannot survive for more than ten days in temperatures around 0°C without food. This biological limitation restricts their geographic expansion, as prolonged cold snaps can lead to starvation or freezing.
Behavioral Strategies for Winter Survival
Since they cannot hibernate, armadillos rely on specific behaviors to manage their energy budget during cold weather. The primary strategy is the utilization of short-term, shallow torpor, which occurs daily to conserve energy when conditions are unfavorable. They use this temporary metabolic slowdown primarily during the cold hours of the night, reducing energy expenditure without committing to deep sleep.
Armadillos increase the time they spend sheltered within their burrows during winter, utilizing this underground refuge for insulation. Burrows often average three to four feet long, sometimes extending up to 16 feet deep, providing a stable, warmer microclimate shielded from surface temperatures. An individual armadillo may maintain multiple burrows for safety and strategic energy conservation.
Because they cannot rely on stored fat, armadillos must forage frequently, even during cold periods. While they are primarily nocturnal in warmer seasons, in winter they shift their activity to the warmest part of the day to seek out insects and invertebrates. This continuous need for food underscores their poor cold adaptation, as prolonged snow or frozen ground quickly leads to starvation.