Slugs are terrestrial mollusks, essentially snails that have lost or significantly reduced their external shells. They are common in gardens and damp environments across the globe. Despite their soft bodies and reputation as mild consumers of decaying matter and plant leaves, slugs possess a surprisingly complex and heavily armed mouth. Their feeding apparatus is designed not for biting or chewing, but for a highly effective rasping action that is key to their survival.
Understanding the Radula
The feeding structure that allows a slug to consume its diet is called the radula, an anatomical feature common to nearly all mollusks. This apparatus is a flexible, ribbon-like membrane made of chitin, not the hard, enamel-coated teeth found in vertebrates. The radula sits atop the odontophore, a muscular base that powers its movement. The ribbon’s surface is covered in hundreds of microscopic, backward-pointing structures called denticles, which function as the slug’s teeth. These denticles are arranged in organized rows, allowing the entire structure to be deployed as a unified scraping tool for processing various food types.
The Astonishing Number of Teeth
The sheer quantity of denticles sets the slug’s mouth apart from most other animals. Depending on the species, a slug can possess anywhere from a few thousand to over 27,000 individual teeth on its radula ribbon. This high count is possible because the denticles are extremely small, often existing at a microscopic scale. These teeth are continuously produced at the back of the radula in a specialized pocket. As the slug feeds, the front teeth are worn down and broken off, mimicking a conveyor belt where new teeth constantly move forward to ensure a sharp, effective dental surface.
How Slugs Use Their Dental Structure
The primary function of the radula is to scrape and file food particles from a surface, rather than to bite or chew large pieces. When a slug encounters food, the muscular odontophore extends the radula out of the mouth opening. The ribbon-like structure then moves back and forth over the material like a file or miniature rasp. This motion shaves off tiny fragments of food, such as soft tissues of leaves, algae, or decaying organic matter, which are carried into the digestive tract. This scraping mechanism explains the signature ragged holes and transparent patches often seen on garden plants, dictating the preferred diet and the characteristic damage slugs inflict.