Currently tarantula turrets state that they are limited to 3 concurrent turrets. There is no way to unsummon short of luring enemies to it to destroy it. This creates a couple flaws:
1. I can summon 3 turrets in close proximity and pull all enemies into that area. I suspect this isn't their intended use.
2. I can't deploy turrets later in the levels if I've used them earlier (again, unless I lure enemies back to destroy earlier ones)
3. I've been able to pull enemies like the dreadnought back through a "trail" of tarantulas I dropped much earlier in the mission.
I suggest instead of a hard cap; adding a time limit to the "life" of a turret. As in, they only persist for 30 seconds or so.
This would practically limit the number of concurrent turrets (based on focus regeneration) while also allowing them to remain useful throughout a mission as I don't suffer from the hard cap being used up by turrets I've left behind.