Snails

So... Im cleaning out a tank that I have had for about 1 1/2 years. The substrate is the same, never been changed. The fish that are in it have been the only fish (some Albino catfish, a Pleco, 3 Australian Rainbows, and an Albino (unknown) Cichlid. I noticed a bunch of very small shells in it; didnt think much of them figuring they may have been in the substrate when I bought it - no real concern... Then I saw a few larger ones 'stuck' to the glass... Snails! I have no idea where they came from, but they are kinda neat.

Does anyone have any experiences like this? I havent added any 'new' fish to any of my tanks in a while, and none of the 'newer' fish I have gotten have been in this tank, nor have they been in a tank along with the current stocklist...

I was thinking of catching some and adding them to my other tanks to help clean the tanks a bit, but figured I would get some thoughts about this before I did it...

This is something that happens to everybody in this hobby sooner or later. I´ve had snails in all my tanks at some point. They get eaten by my cichlids in the tanks, but there are still several of them behind the background in my 66 gallon.