The Keel Bug is a deleted Covenant species seen in the Halo 2 Collector's Edition video. It was supposed to come into the battlefield, cut up dead bodies into sections, and then fly off with them, as a way of cleaning up the bodies. They were originally going 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.
The concept of an insect-like creature as an enemy may have led to the design of the Yanme'e that appears in Halo 2 and Halo 3. The Drone picking up the Marine in the level Crow's Nest may be a reference to Keelbugs.
While developing the Halo games, Bungie, 343 Industries and Ensemble Studios have had to cut some content, such as vehicles, gameplay, and story elements, from the final products. Much of this content has been confirmed by videos and commentary in special edition DVDs, interviews with developers, and released concept art.