Slugs are fascinating invertebrates with a unique relationship to water. Unlike many animals that actively drink, their hydration is a process deeply integrated with their environment and body structure. Their survival hinges on maintaining a delicate balance of moisture, which they manage through specialized biological features and behaviors.
How Slugs Obtain Water
Slugs primarily obtain water through absorption directly across their permeable skin. When dehydrated, these gastropods exhibit a behavior called “contact-rehydration,” where they flatten their bodies against moist surfaces, such as wet soil or leaves. This allows water to rapidly enter their system, particularly through the epithelium of their foot. Research indicates that during this process, the intercellular spaces between their epithelial cells can enlarge, facilitating the bulk flow of water into their bodies.
A significant portion of a slug’s hydration also comes from the food it consumes. Slugs feed on decaying plant matter, fungi, and algae. Their characteristic slime plays a crucial role in water intake and retention. This hygroscopic mucus actively absorbs moisture from the environment. Produced by specialized goblet cells, the slime can absorb hundreds of times its own weight in water, which is then absorbed by the slug’s skin.
The Importance of Moisture for Slugs
Moisture is important for a slug’s survival. The slimy coating that covers their bodies is important for movement, acting as a lubricant that allows them to glide smoothly over various surfaces, including rough terrain and even vertical structures. This constant production of slime necessitates a continuous supply of water.
Slugs breathe through their skin. This gas exchange requires their skin surface to remain moist; a dry slug cannot effectively absorb oxygen or release carbon dioxide. All their internal physiological processes depend on a hydrated state. Their preference for damp, shaded environments, such as under rocks, logs, and decaying vegetation, directly reflects this strong need for constant moisture, as these habitats minimize water loss. Slugs are predominantly nocturnal, a behavioral adaptation that allows them to avoid the sun and wind.
Coping with Dry Conditions
When faced with insufficient moisture, slugs employ strategies to survive. They instinctively seek out damp refuges, burrowing under rocks, logs, or into the soil to escape drying conditions. This behavior helps them conserve their body water by avoiding direct exposure to dry air and sunlight.
For prolonged periods of drought, slugs can enter a state of dormancy known as aestivation. During aestivation, they reduce their metabolic rate and seal themselves within a protective layer of mucus. This hardened mucus cocoon acts as a barrier, trapping moisture. A slug experiencing dehydration will visibly shrink and become inactive, appearing shriveled. While they possess a notable ability to recover from considerable water loss, potentially up to 60% of their body water, severe or prolonged dehydration can be fatal, making them feel hard to the touch.