Right hand image taken 32 minutes after the left hand one.
After one swing of the head (see 39Ch 39 Cepaea hortensis feeding on dried flour paste on glass. Pennine foothills, V.C. Derbyshire, England. August 2018. ), the animal advanced slightly so the next swing was on new food leaving no waste except a narrow strip containing the triangles formed by the radula tip (1). On horizontal glass, the snail shifted periodically to clear a rounded area. In 32 minutes the area cleared of flour increased by about five times the basal area of the shell; equivalent to the area of the shell every 6 minutes. In the wild on surfaces covered in algae, a linear radual track is often seen; see 41Ch 41 Cepaea hortensis feeding marks on dried flour paste on glass. Pennine foothills, V.C. Derbyshire, England. August 2018. .