I agree with rossi. i have seen them mate, and the other day, i just saw one giving birth to small clear eggs.Had them for about a month, and still, they are minimal, and they do eat lots and lost of algae, they even beat my SAE since they actually eat all the way to the glass, where as my SAE only eats the upper half and leave the "older" algae intact.
My dad got them from his friend who is a professional aquarist. he keeps plants, too, so i guess they are not harmful to plants...anyway, does anybody really know what is the name of this snail, are they a type of ramshorn????