The bugs have found our homeworld and are invading by the swarms! We have an experimental bio-weapon that can kill all the bugs without killing a single human. We need you to hold up our primary millitary base for 30 minutes while the the genetic bio-weapon is prepared. We must keep our base operational until the the biological weapon of mass bug destruction can be delivered!
You will see every single type of zerg in the starcraft game, from drones + swarmlings to zerglings + hydralisks + roachers to brood lords, brutalisks, omegalisks, and leviathans. It starts out with drones only and a new bug type evolves every 60 or 120 seconds. The bug rush is continual and will never stop.
At least 1 Bio-Dome must survive for synthesis of the genetic bio-weapon or you must destroy (nuke) all 8 of the bugholes. Killing some of the bug holes will bottlneck the flow of bugs and also reduce the flow somewhat.