Feeding and Nutrition

Finding Food

Weinbergschnecke bei der Nahrungsaufnahme.
A Roman snail feeding. The small tentacles are used to investi-
gate the food. [CK]

Roman snails and all their relatives of the helicid family (Helicidae, also see Systematics) exclusively are plant eaters that may crawl amazing distances between resting places and feeding places. Roman snails, though, very rarely appear in numbers comparable to the Durham or Lusitanian slug (Arion vulgaris), so they can hardly be called a garden pest.

Its relative, the brown garden snail, on the other hand, in fact may well be called a garden pest, where it has been introduced into a new environment, such as in the United States.

  Weinbergschnecke knabbert an einem Blatt.
A Roman snail eating a leaf of green food. It pulls the leaf into
its mouth using the radula and then with the jaw cuts a piece
off it. [RN]

On the search for food the Roman snail orientates using its tentacles. The large one sweeping the environment in a searching motion, give the snail an overview over its immediate surroundings. Sense cells, especially on the smaller tentacles search for promising traces of food smell. Taste receptors on the lips mainly are of use to investigate potential food on a close distance.

It has been proved by experiments that Roman snails are able to find food in some distance and then directly crawl there. It is, however, difficult to define precisely Roman snail's food preferences. Limp food is generally preferred to fresh green plant parts. On a snail farm, where the snails are fed with fresh green plants growing in their enclosure, limp food must be added.

Other than many slug species, Roman snails almost never eat mushrooms and fungi. The assumption that Roman snails feed on the egg batches of other snails is possibly based on cannibalism sometimes occurring in the hatchery holes. The assumption is, however, completely untenable.

The Process of Eating

Like all molluscs the Roman snail as well uses a specialised organ to take in and process food, which is as unique in the animal kingdom as it is typical for molluscs.

Schematische Ansicht der Radula und beteiligter Organe.
Schematic view of the radula and participant organs. A: Mouth
opening; B: Jaw; C: Rasp plate; D: Radula gristle.
Source: Forcart, L.: "Schnecken und Muscheln" (1947).

How a Roman snail uses it can best be seen, when it eats at the edge of a leaf. Then the snail can be observed pushing out its tongue and then pulling a piece of food into the mouth. If this process is recorded on tape and replayed with enhanced volume, a distinct rasping sound can be heard. With the naked ear the sound can also be heard when the snail cleans its shell by licking its surface.

Only under a microscope it can be seen, that a snail's tongue in fact is a rasp tongue or radula, on which there are thousands of tiny little teeth in lateral rows. Actually a Roman snail's radula works like a bucket-wheel excavator: A tissue band armed with teeth moving over a gristle core is pulled through the food and so digs small particles from it, then transporting them into the gullet. In the rear part of the radula, new toothlets are formed, so those worn down can be replaced continuously.

A snail's radula is adapted to its food as well as is a mammal's set of teeth. So its numerous toothlets of equal shape show that a Roman snail clearly is a herbivore.

Thanks to their radula, snails are among the few invertebrates that are able to grind their food before swallowing it. Arthropods, for example, have either to rip their food apart, like a crab, or to digest it externally by injecting digestive fluid into the prey's body.

Movie: A snail feeding on a piece of cucumber. [RN] MOV file, ca. 4,5 MB.