So if I have 3 1|1 swarms and I kill 1 I would have 2 1|1 swarms and 3 2|2 swarms?
I am not sure it needs the +1|+1 to be potent.
As it stands right now, I think I prefer the second of my two options.
So if you have 3 1|1s and you kill one, it would die and the other 2 would create a 2|2 each.
This leaves you with 2 1|1s and 2 2|2s
The problem is after that. It might increase a bit too quickly. If I kill a 2|2 now, I would get back 3 3|3s, which might accelerate out of control.
My other idea is to make it leave behind 2 copies of itself if it dies. This way at 3 swarms the result is the same, but at the next tier it would only leave behind 2 copies rather than 3.
The downside to this is that it would be unkillable, but it's not like it's easy to remove right now one way or another.