Za'zayara-pattern Harvester

A Type-58 Ultra-Heavy Site Excavator/Embedded, colloquially known as the Harvester, is a Covenant walker used during large-scale excavations and in the search of artifacts. An exceedingly rare sight in the field, one was used by Jul 'Mdama's Covenant during their occupation of Requiem.

Design
Harvesters are the biggest Covenant land vehicles to date, with only the "Super" Scarab being comparable in size. Generally used in long-term invasions, they are not commonly seen by UNSC personnel. Much like the Scarab, it is composed of a meta-colony of Lekgolo known as Sbaolekgolo; this is evident from exposed Lekgolo worms seen in its interior.

While all Covenant technology shares a generally organic design aesthetic, the Harvester's features are significantly more ornate and conspicuously insectoid than most Covenant constructs. It is much more beetle-like in appearance than the Scarab due to its overall shape, heavily textured outer "skin" and a hatch at the front of the machine that resembles a mouth and eyes. The interior is composed of multiple massive chambers that resemble dark subterranean caverns, linked together by smaller hallways and illuminated with pale green light.

History
A Harvester was once encountered during the Requiem campaign, where it was disabled by Fireteam Switchback, who mysteriously vanished in the firefights afterwards, leaving no bodies or signs of struggle, only their IFF tags. Fireteam Crimson was sent in to investigate. Crimson managed to kill the remaining crew of the Harvester and further disabled the walker by destroying several consoles inside.

Sometime later, the Covenant re-took the Harvester and captured several doctors to re-activate the walker, but they were not successful because the power supply was destroyed. When Requiem was put on a collision course towards the star it was orbiting, Fireteam Crimson was sent to retake the Harvester and use it to reach one of the artifacts that was preventing the from leaving the planet. After stealing the power source from a Lich, Crimson returned to the Harvester and activated the walker. Crimson then used the Harvester's plasma drill to excavate a tunnel deep enough to reach the artifact and shut it down. The Harvester was destroyed when Requiem was consumed by the star Epoloch.

Trivia

 * Throughout the Halo 4: Official Game Guide's digital Spartan Ops walkthrough, the Harvester is constantly referred to as being a Forerunner construct.
 * The Harvester is the third known Covenant vehicle that isn't named after an insect or spectral entity. The other two are the Type-25 Chopper and the Type-52 Prowler.

List of appearances

 * Halo 4
 * Spartan Ops