Bioerosion of shells by terrestrial gastropods

Empty shells of terrestrial gastropods remain intact and become fossilized only under particular conditions. The usually thin shells are readily disso lved by rainwater, a process starting often during life. Results indicate t hat with this chemical weathering they may lose some 1% in weight per month . But this is not the only process by which shell biominerals disappear. Du ring field experiments, living terrestrial gastropods have been observed to actively remove calcareous material from empty shells apparently to use fo r building their own shell. Empty shells lost similar to 30% of their weigh t in 2 months, indicating this process to be much more important than simpl e dissolution, and explaining the rapid disappearance of empty shells in th e field. Previously, mainly anecdotal mention has been made of this shell s craping. Bones of birds were not scraped by terrestrial gastropods; they lo st similar to 1% in weight per month at the start due to chemical weatherin g alone, but weight loss decreased with time and was only 6.5% after 16 mon ths.