If an infection form takes over a body that is unsuitable for combat, or once a combat form is damaged beyond usefulness, it becomes a carrier form. Carrier forms perpetuate the Flood species by acting as incubators for new infection forms and keeping them safe until they're fully developed. Once the infection forms are ready, the carrier simply explodes, sending the new infection forms flying into the air. As soon as the new parasites are released, they start searching for something to infect. It should be noted that carriers will sometimes not wait until full maturation has occurred, and will simply get close to an enemy and explode, sending the infection forms flying at the unsuspecting and often damaged enemies. These should be considered dangerous even though they may not have any other means of inflicting damage.
The Plasma, brute spike, and Firebomb grenade will destroy the infection forms before they can come out making it much less of a threat.