From Halopedia, the Halo wiki
"Locust" is the name applied to a series of Covenant quadrupedal mining platforms.
Like all known Excavators, the Locust is named after an insect rather than a supernatural entity like most Covenant vehicles. Locusts are members of the grasshopper family that are infamously known for rapidly stripping fields of crops. The walker's similar "building killer" usage may be the reason for the vehicle's name.
List of appearances