Soldier parasites were a type of bluegill parasite, the lowest caste which did the bidding of queen parasites and spawnmothers.

Soldiers were either spawned directly from a spawnmother or were amongst the fifty or so children of a queen parasite. They could be controlled or instructed via telepathic or short range pheromonal communications with their queens and spawnmothers and did their leaders bidding. (DS9 novel: Unity)

For the general capabilities of bluegills see the main bluegill article.