Country diary: these wrinkled rock stars are boring little molluscs

Whitburn Rocks, Sunderland: Tunnelling into the soft limestone helps them avoid predators, but they can grow too big to escape their sarcophagusSmall boulders at the top of this beach are often drilled with smooth-sided holes, as wide as my smallest finger, and some rattle when they are picked up and shaken. The sources of the sound, almost hidden in the tunnels, are paired, empty shells of dead wrinkled rock borers, Hiatella arctica.These bivalve molluscs, growing to about an inch long, should have the safest homes in their lower shore habitat. Once they've survived a perilous infancy as planktonic larvae, they settle on the surface of rocks and, by dint of secreting a weak acid and constantly fidgeting, use their toughened, ridged shells to bore into soft limestone. Some boulders become the geological equivalent of Emmental cheese, riddled with holes. Continue reading...