hiya, im not sure wot sort of snail u have, but depending on the type, and the size, they cud just think its going to eat their food, or just dnt like it being in the tank.
it mite be a gud idea to post a pic of the snail if u can.
Also, what sort of damage have they done to the snail ? their shells sud protect the actual snail fairly well, depending on how aggressive the kribs have been towards it.