Most rock eaten by a land animal

Two small species (c. 1-cm/0.4-in-long) of rock-eating snail, Euchondrus albulus and E. desertorum, native to the eastern Mediterranean and Middle East use a rasp-like tongue (radula) to consume endolithic ("inside rock") lichens that live around 2 mm (0.08 in) below the surface of limestone rocks. The snails digest the lichens and in the process excrete ground-up rock, among other things. A study conducted in the Negev Desert in Israel, published in the journal Science on 29 May 1987, documented that a single snail can eat nearly 5 g (0.17 oz) of rock in a year (with roughly 21 snails living per square metre), turning rock into soil at an annual rate of up to 1.1 tonne (1.2 US tons) per hectare. This amount of soil formed by “bioerosion” equals that blown into the desert by wind every year - in other words, snails in this region account for around half of all new soil formation in their locality.

Some of the nitrogen from the lichens is used by the snails for growth and reproduction, but some also gets excreted, fertilizing the desert (22-27 mg nitrogen per m2 per year). This contributes around 11% of total soil nitrogen inputs, 18% of net soil inputs and a minimum of 27% of the nitrogen annually accumulated by endolithic lichens from dust.

Closely related snail species in the Dolomites, located between Austria and Italy, also eat rock but are less abundant and bioerosion rates are not measured. Mollusks, chitons and isopods etc erode rock in aquatic environments, including a new species of rock-eating clam (Lithoredo abatanica), a type of freshwater shipworm reported in the Bohol province in the Philippines in 2019. Other organisms such as lichens (the food source of the snails) also erode rock on land, but as far as we know these snails are terrestrial animal champions in terms of amount of rock eroded per unit area, with the added bonus of simultaneously fertilizing their desert home in the process.