I put some Olive Nerite Snails in my tank about 2 days ago. Right now two of the snails are just on top of each other under the plants and stayed that way for about 30 mins. I dont have a picture of my snails but its similar to this picture
Nerite snails can't complete their lifecycles in freshwater, so don't worry about becoming overpopulated! They can lay eggs (sorry, I don't know if yours are mating), but these eggs won't develop or hatch. At least, that's what I've read, and the ones I had never bred.
LOL! I don't know why but I just think it's kind of crazy to imagine two snails mating. I just never really sat down, and actually thought about it. Kind of weird!