Geologists in the early 19th century debated the origin of deep tubular holes bored into hard limestones in several European countries and decided that land snails, especially the ‘grove snail’ Cepaea nemoralis, were responsible. Recent research on the Mendip Hills in England confirms this view. The fact that snail holes are bored in subaerial conditions at a maximum rate of c. 1.5 mm in 10 years makes them a useful tool in karst landform interpretation. The local Ipswichian topography of a Mendip closed basin is reconstructed assuming that hundreds of borings in Twin Titties Swallet are pre-Devensian snail holes.