well if you def dont have any snails in the tank and its really hard to sex them they could be trying to eat each other its what they do at point of no food left
they do on the other hand eat any left over food or algae but they prefer live food like helpless fry , snails, fish eggs
if anything i would get a breeding tank buy some plants and hope they got snails in it
i know cause i had 4 till one day they felt so dumb they couldnt find a suitable snail to eat cause they are shy about eating another snail thats 3x or more of its size
so one ate the other and later on i am guessing out of revenge another came by and finished the hit..
so i got two left and they go hunt when the lights are off..
your best bet when getting these type of snails is to make sure you have spare snails to breed that way you always have more..