I recently had an outbreak of small common snails, so I go me 5 assasin snails.

They did the job admirably, but after a couple of months there was no snails left, and I introduced nerite snails (pretty and eat algea).

For the time being I put the assassin snails into an enclosure and feed them protein pellets, at least until the nerite start to reproduce.

That is when I noticed something odd. I found 2 of the snails stuck to each other, and they seemed happy that way. A little while later I found 2 others the same way. I had noticed them pairing, but thought it might be a fluke. I thought the 5th one died since I hadnt seen it in a while, but once I setup the enclosure, it came out of hiding and raced over to it, even though by now the tank was full of prey items.

Assassin snails seem to have some complex social behavior that does not seem described in research so far.