Illuminate should have an effect that activates during battles, but I'm not sure what it should be. Stench and Pickup were given in-battle effects, so I don't see a reason not to give Illuminate the same treatment.
As XanderO pointed out, Swarm isn't useless entirely; it works in the same way as Overgrow, Blaze and Torrent, but for Bug moves. It's viable on Scolipede because it can spam 270 base power Megahorns (taking STAB and the Swarm boost into account). The same applies to Escavalier.