Two broodlings are created using a queen's Spawn Broodling ability and last a maximum of 180 seconds. Broodlings can wreak havoc in a siege tank artillery line. The initial spawning destroys one tank, while the other closely packed tanks damage each other via splash damage as they fire on the broodlings.
It is even possible to spawn broodlings from a broodling.
In Dark Origin, slaying all the ursadons creates a broodling from one of their stomachs that does not have a 'countdown' life span. Aside from that it behaves like any other broodling and may be mind-controlled by a dark archon.