Keelbug
From Halopedia, the Halo wiki
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 flies off with them, as a way of cleaning up the bodies. They were originally to be used in Halo: Combat Evolved as a clever method of removing NPC corpses to free up memory. This race would have been a gruesome addition to the Covenant races.
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 can’t access, there are some bugs crawling around. These may be Keelbugs cleaning up the mess in the prison cell.
