SHELL STRENGTH OF MUD SNAILS (ILYANASSA-OBSOLETA) MAY DETER FORAGING BY DIAMONDBACK TERRAPINS (MALACLEMYS-TERRAPIN)

Diamondback terrapins (Malaclemys terrapin) do not eat the common and abundant mud snail (ilyanassa obsoleta) even though terrapin diets are dominated by similarly sized gastropods. To resolve this paradox, we tested a structural defense hypothesis as the potential deterrent agai nst predation. We compared resistance to compressive force of ilyanass a and three invertebrates (Littorina irrorata,) Uca spp, and Callinect es sapidus) that terrapins commonly eat. Ilyanassa shells were 2-3 tim es more resistant to crushing than the other prey. High processing cos ts for mud snails (in terms of structural resistance to crushing) may deter predation by terrapins despite the low search costs and equivale nt energetic returns relative to alternative prey items.