The Giant Ant Queen is an enemy found within The Gutter surrounded by poison emitting foes. It exudes a light blue gas that cures the player of poison if they are currently aflicted by it, though if the build up has not passed the threshold to cause damage it will not remove the build up. The Corrosive Urn is said to use the extract of ants, likely this is one of these such ants. This enemy resembles a large insect with sharp black legs and a long fat body. It is incapable of attacking and will not respond to even being damaged aside from its death animation.
The name of this creature comes from a translation of a name by Namco Bandai that was given to the creators of the Dark Souls 2 Guide. Around fourteen minutes in an explanation of this is given in this video.