Radula

Strange marks have been appearing all over our patio.  These lines of symmetrical shapes, making up seemingly random patterns over the surface of the slabs have been appearing over-night all Summer.  Closer inspection reveals that they are made up of tiny, triangular shapes scraped into the dirt and algae.

They have been made by snails and slugs as they slime their way across the patio in search of food.  Molluscs such as these have strange mouth-parts known as Radulae.  Each Radula is used rather like a tongue (although it is not a tongue) and is equipped with hundreds of minute 'teeth' or Denticles with which it scrapes away at it's food.  This scraping leaves behind a typically triangular mark where the food has been removed.

This is an incredibly effective way of feeding, as anyone who has had the plants in their garden devastated by slugs and snails will testify.  It probably also indicates that our patio needs a good clean!