These prophet-like creatures pulsate low droning chants that can be focused into sonic like attacks. They usually lurk in the backdrop of enemy ranks, carrying weapons such as the Gorgon Pistol and Poison Grenades. The real threat with these demons is that they can revive fallen comrades, which makes advancing through enemy lines an even more difficult task. A piercing scream heralds these resurrections, that knocks you to the ground if you're standing close enough to the Kantus. Note that enemies heavily mutilated during the process of their (un)fortunate demise are unable to be resurrected, i.e Longshot headshots, grenades, the Lancer's chainsaw etc.
To take these guys on, I suggest the Gnasher Shotgun and run towards them, beware though,as their screams can knock you down and make you easy meat for other Locust. Using the Shotgun, melee them and follow up with a quick shot to the face. Sniper Rifles work well from a distance. NEVER attempt to use the Shotgun against them on Insane, their Pistol shots will kill you before you get in spitting distance of them, and even if you survive it will be quite a task to kill them. It is suggested you use the Sniper against them on Insane. The Lancer Assault Rifle is also a nice weapon against them on all difficulties.
Note that the Lancer's chainsaw is also usable against them. Approach them with caution however.