Observations of radula tracks in the wild (Craik & Anderson, 2018) show that the track of an unobserved gastropod species was linear with few radula strokes per head-swing (1) on surfaces poor in alga not worth expending energy on, and changed immediately (2) on reaching an alga-rich area to head swings five times wider with many more radula strokes per swing (3) and a sinuous route, avoiding previously cleared tracks, to clear a non-linear patch of algae (4).
The radula strokes also removed the weathered grey surface of the butyl to expose paler fresh material.
41.1 Cepaea hortensis album. Radula track of unobserved species of gastropod on a pale butyl-rubber roof surface partly covered with algae. Magnified section on right. Oban, Scotland. September 2018. © C. Craik.
