Millipedes are terrestrial arthropods, known for their elongated, segmented bodies and numerous legs. Despite their preference for damp environments, they cannot breathe underwater. Their physiological design is adapted for life on land, meaning the respiratory system depends on direct contact with atmospheric oxygen. Submerging a millipede in water disrupts this process, leading to suffocation.
The Millipede Respiratory System
Millipedes rely on a network of internal tubes called the tracheal system. This system consists of tiny, air-filled tubes that branch throughout the body, delivering oxygen directly to tissues and organs. Air enters this internal network through small external openings located along the sides of the body, known as spiracles. These spiracles are found in pairs on most body segments, acting as ports for gas exchange. This design is highly efficient for a small creature living in an air-rich environment, but it requires a continuous supply of atmospheric air to function properly.
The Fatal Impact of Water Submersion
The terrestrial nature of the millipede’s breathing apparatus explains why submersion in water is lethal. When a millipede is underwater, the external openings of the spiracles become blocked by the surrounding water. The surface tension of the water seals these openings shut, preventing air from entering the tracheal system.
This blockage immediately halts gas exchange, causing the millipede to suffocate. Unlike aquatic organisms, millipedes lack gills or specialized structures that can extract dissolved oxygen from water. Their tracheal tubes are designed only to handle air, not water, making the system useless when submerged.
While some species possess anatomical mechanisms to temporarily close their spiracles, this action only delays oxygen deprivation. Once the air supply is cut off, the presence of water overwhelms the air-dependent system, leading to respiratory failure.
Millipede Habitats and Survival Time
Millipedes are typically found in moist, dark environments, such as decaying leaf litter, under stones, or damp soil. They require high humidity because their respiratory system is constantly open to the air, resulting in a significant loss of body moisture. This threat of desiccation is why they are strongly associated with damp habitats.
If an average millipede is accidentally submerged, such as during heavy rain or a flood, its survival time is generally limited to minutes or a few hours. The ability of some species to overlap their body segments can temporarily seal the spiracles, delaying death by conserving air inside the tracheal system. Certain specialized species, however, have evolved adaptations that allow them to survive extended periods underwater during seasonal flooding. This endurance is attributed to structures that trap a film of air around the body, functioning like a temporary physical gill, or an oily outer layer that prevents water from contacting the spiracles.