杏吧原创

I wonder whether anyone knows what this pattern is that I found on my north-facing window sills earlier this year (see Photo, right)? It looks like some kind of footprint and seems to come in two sizes. A few months on, it鈥檚 still there鈥�

鈥� The pattern was made by snails or slugs as they grazed on algae growing on the sills. Slugs and snails possess a set of tiny teeth embedded in a muscular, gristly structure which forms what is called the radula (see my images of radulae at ). Muscular action drags the band of teeth over the substratum, removing food which is then ingested.

Each species of snail has its own characteristic pattern and style of teeth, and this can be used to help to distinguish between species. Similar patterns can be found on rocks on the seashore which grazing limpets and periwinkles have zigzagged over, removing settled algae and other food as they do so.

Gerald Legg, Keeper of Natural Sciences, Booth Museum of Natural History, Brighton, UK

鈥� The patterns have been produced by snails grazing on algae. The snail scrapes off the algae with its radula 鈥� a sort of tongue with teeth. Hence the proverb Tavas medall ew howlsethas an bullhorn, which in English becomes 鈥淎 smooth tongue is a snail鈥檚 undoing鈥�.

David Ridge, London, UK