Keelbug

The Keel bug is a deleted Covenant race seen in the Halo 2 Collector's Edition Video. It was supposed to come into the battlefield, cut dead bodies into sections, and then fly off with them, as a way of cleaning up the bodies. They were originally to be used in Halo:CE as a clever method of removing NPC corpses to free up memory.

The concept of an insect-like creature as an enemy may have led to the design of the Drone that appears in Halo 2 and Halo 3.

In the Halo 2 campaign, when you must free the marines from the prison blocks, outside one of the prison room doors that you cant access, there are some bugs crawling around. Theese may be Keelbugs cleaning up the mess in the prison cell.