A river worm eats rock to make tunnels.

Rock-eating shipworm — Abatan River, Bohol, Philippines

In a Philippine river, scientists described a shipworm that bores into limestone instead of wood. As it digs, it swallows the rock and crushes it into fine sand, leaving a honeycomb of tunnels in the riverbed. In its 2019 formal description, this rock‑by‑ingestion strategy was the only one then known in animals, setting it apart from both wood‑boring shipworms and other rock‑borers that do not eat what they excavate.