With how the Locust look and act, most players would agree that 'Locust' is a pretty spot-on name for the horde of enemies; they normally appear as a swarm of enemies and they have somewhat of a bug inspired look. However, when the game was first planned, and already somewhat
in development, developer Epic Games had another name in mind for the antagonists; The Geist.
Another word for 'Ghosts,' Epic Games had developed a lore around around The Geist as almost mythical creatures, similar to ghosts. However, developers n-Space released their first person action game Geist in late 2005, so Epic Games, fearing that it might be too much of a similarity, quickly decided to change the name, eventually deciding on the one that we all know and love today. Luckily, the game wasn't too far into development, so not much had to be changed in order to accommodate the last minute decision.