Millipedes are fascinating arthropods recognized by their elongated, segmented bodies, belonging to the class Diplopoda. They are characterized by having two pairs of jointed legs attached to most body segments, a feature that distinguishes them from their centipede relatives. Like all arthropods, millipedes possess a hard, external exoskeleton that cannot stretch to accommodate growth. To increase in size, they must undergo a biological process called ecdysis, commonly known as molting, where they shed the restrictive outer shell. This shedding is necessary for millipede development and allows for the repair of minor physical damage.
Molting Frequency Based on Life Stage
The frequency of molting is highly dependent on the millipede’s age and developmental stage. Juvenile millipedes, often called nymphs, molt much more frequently than adults due to their rapid growth phase. They typically go through numerous molts, often seven to ten times, before reaching their full adult size. This pre-adult process can take a significant amount of time, sometimes spanning two to five years, depending on the species and environmental conditions.
Each successive molt adds new body segments and pairs of legs, gradually increasing body length and complexity. Once a millipede reaches its maximum size and sexual maturity, the molting frequency sharply decreases. Adult millipedes may only molt once a year, often coinciding with favorable environmental conditions, or they may cease molting entirely. Younger millipedes spend a greater percentage of their time burrowed underground compared to older, more surface-active adults.
The Physical Steps of Ecdysis
The process of ecdysis begins with pre-molt signs, such as reduced activity, a change in body color, and refusing to eat. The millipede then burrows deep into the substrate to construct a secure, oval-shaped molting chamber, often bound with silk or oral secretions. This protective chamber is essential for maintaining the high humidity necessary for the old exoskeleton to separate from the underlying new one.
Once inside the chamber, the millipede sheds its old cuticle, a delicate process that can take several days to weeks, or even a few months for larger species. Immediately following the molt, the millipede enters the teneral phase, where its new exoskeleton is soft, pale, and highly vulnerable. To hasten the hardening of the new shell and reclaim nutrients, the millipede consumes its discarded exoskeleton, known as the exuviae. This consumption is important for recycling the calcium compounds needed to stiffen the new, larger shell.
Essential Environmental Support
Successful molting hinges on specific external factors within the millipede’s environment. The quality and depth of the substrate are paramount, as millipedes require a sufficiently deep layer—ideally at least one to two times their length—to construct protective molting chambers. This substrate should be composed of rich, decaying organic matter like flake soil, wood, and leaf litter, which also serves as their primary food source.
High environmental humidity is another requirement, with many species thriving in conditions ranging from 70% to 80% relative humidity, maintained through proper substrate moisture. The moist substrate prevents the millipede from drying out during the vulnerable shedding process, which can lead to fatal molting failure. An adequate supply of calcium is necessary for the calcification and hardening of the new exoskeleton. This mineral can be provided through the substrate in forms like crushed limestone, cuttlefish bone, or calcium powder, ensuring the millipede rapidly develops its defensive, rigid outer shell.