User blog comment:Dragonzzilla/ME3 Multiplayer DLC I Ideas/@comment-4967682-20120430025126/@comment-1888392-20120430025759

Keep in mind, PHANTOMS have moderate barriers and moderate health and they're a b*tch to kill. Moderate Barriers might be reserved for Guardians.

The Swarm Grenade is the Collector version of the grenade. Instead of the traditional grenade, when the grenade "detonates", a swarm of Seekers occupy the grenade's "blast radius". Any player that draws too close to the cloud will suffer damage.