Millipedes are detritivores that break down decaying organic matter, enriching the soil in gardens and forests. These cylindrical invertebrates are often mistaken for worms with too many legs. When seasons change, leading to cold or drought, many people wonder if millipedes hibernate due to their disappearance.
Clarifying Dormancy Versus True Hibernation
Millipedes do not undergo true hibernation, a complex physiological state reserved for certain mammals. True hibernation involves a regulated drop in body temperature, slowed heart rate, and profound metabolic depression, controlled by internal mechanisms. As ectotherms (cold-blooded), millipedes lack the biological machinery to regulate their temperature and metabolism in this controlled, long-term manner.
Instead, millipedes, like many other invertebrates, enter a state of dormancy, which can manifest as one of two distinct forms. The first is quiescence, a direct and immediate response to unfavorable environmental conditions like sudden cold or dryness. This state is maintained only as long as the adverse conditions persist, and the millipede will quickly resume activity if the weather temporarily improves. The second, more programmed state is diapause, a genetically-fixed, hormonally-controlled arrest of development or reproduction often triggered by environmental cues like changing day length. Diapause is a prospective dormancy, induced before adverse conditions arrive, preparing the millipede for survival through predictable seasonal challenges.
Environmental Signals That Trigger Seasonal Inactivity
The primary triggers for millipede inactivity are not solely based on temperature, but are also critically linked to moisture levels. Millipedes have a soft exoskeleton and are highly susceptible to water loss, making them exceptionally dependent on moist environments. A lack of moisture, or drought, can force them into dormancy just as effectively as a temperature drop.
When temperatures fall below a certain species-specific threshold, often near freezing, or when the soil begins to dry out excessively, the millipede’s body signals the need for retreat. Field experiments have shown that a lack of surface moisture can cause a rapid onset of quiescence, even more so than moderate temperature shifts. Conversely, a rapid return to moist conditions, such as after a rainstorm, can quickly break the dormant state, leading to sudden mass emergence.
The combination of cooling temperatures and decreasing moisture in the fall is a powerful cue for millipedes to seek protected overwintering sites.
Survival Strategies: Where Millipedes Go
To survive cold or drought, millipedes rely on behavioral strategies focused on finding shelter. Their most common strategy involves downward migration into the soil. They burrow deep into the substrate, sometimes several feet down, seeking stable temperatures and humidity below the frost line.
Once in these sheltered microclimates, their metabolism slows significantly, and they cease feeding entirely, subsisting on stored reserves until favorable conditions return. The millipede remains curled up in a tight coil, a natural defensive and moisture-conserving posture, throughout the dormant period.
Some species also engage in aggregation, gathering in large numbers in sheltered locations such as under rocks, deep within compost piles, or inside rotting logs. This mass clustering helps to conserve moisture and potentially share what little warmth is available from decaying organic matter. These adults remain inactive through the winter or dry season. They re-emerge in the spring or when the wet season begins, signaled by rising temperatures and the return of adequate surface moisture.