Add infestation, drop spawning. Probably modify the absorb magic and dampen spell abilities (at least the DCs) as well as the shocking touch. Sound right?
Let's fill in those DCs.
Individual leech:
absorb magic - DC 10 everywhere, and add a line that it's Cha-based.
Swarm:
same thing, just DC 13.
Looks pretty good, generally speaking.
So I think it just needs Distraction and flavor/tactics text for the swarm.
Must have missed a Spot check.
SR 21 seems fine for the swarm.
Do they need anything else?