Unggoy, also known as Grunts by many individuals, are a sapient species of squat bipedal xeno-arthropodal vertebroid lifeforms from the planet Balaho. In 2142, the Unggoy became the fourth species to be assimilated into the Covenant. During their tenure in the hegemony, Unggoy were always the lowest-ranking species in general terms, and were frequently mistreated by members of almost every other race, especially the Kig-Yar, Jiralhanae, and Sangheili.
Unggoy were primarily used by the Covenant as laborers or—in combat situations—cannon fodder. They are commonly referred to as "Grunts", mainly because they are considered weak compared to other former Covenant species and because they performed the majority of the labor required by the empire.
The taxonomic classification of the Unggoy has been a source of some confusion for the United Nations Space Command. Because they possess exoskeletons, they have been identified as being analogous to Earth arthropods; despite this, the Unggoy are actually a vertebrate species. The UNSC misclassified the species as arthropodal due to their physiological similarities to terrestrial arthropods; among other differences, the Unggoy circulatory system is apparently closed as opposed to the open systems characteristic of many arthropods. More accurately, the species should be considered xeno-arthropodal vertebrates which possess substantial—albeit hypothetical—genetic influences from primate-like amphibians that once dwelt in Balaho's aphotic zones. This taxonomically incorrect nomenclature persists as late as 2557 as an ad hoc identifier, though the pressures of the Human-Covenant War and reconstruction have made such concerns trivial at best.
Unggoy share a number of features with different animal species on Earth. Like primates, they walk both bipedally and with the aid of their oversized forearms. However, their bodies are armored with a hard exoskeleton as with crabs and insects. Their mouths have a set of small, pointed teeth, much like reptiles. Unggoy are on average about four to five feet tall and are relatively weak compared to other sapient species. The Unggoy have flat, three-toed feet, with another toe on the back of their feet. Although they can easily walk upright on two legs, they may often use their arms to move in a quadrupedal fashion. While carrying armaments, they are forced to walk upright so that they may support their weapons with their hands, but while trying to flee, or while patrolling without a weapon drawn, they use their oversized arms as forelegs to add speed or stability to their gait. Their eyesight and hearing are average, and seem to have a very well-developed sense of smell, sometimes sniffing the air to detect traces of foes or hidden enemies. This is facilitated through the olfactory membranes installed in their masks. Unggoy have oversized forearms, while their upper arms and thighs are relatively small. This has allowed them to be quite excellent climbers over rocky terrain, although they are rather clumsy when walking upright. Their large arms help the Unggoy in hand-to-hand combat and scaling heights, but make movement around tight corridors or manipulation of small, delicate objects difficult. To protect themselves from the voracious predators of Balaho, the Unggoy have a rigid exoskeleton that is lined with sharp barbs that covers large portions of their backs, arms, and legs. They also have an astonishingly fast finger reflex speed, as they can fire a plasma pistol at almost the same rate a Sangheili can with a plasma rifle.
Unggoy also have thick, bioluminescent, light-blue blood, possibly a result of methane-based proteins in the blood to facilitate methane-based respiration. Like Earth's horseshoe crabs, it is possible that their blood is blue due to high copper content. They also possess yellowish-green colored viscera, visible in an unused texture seen when an Unggoy is decapitated via glitches.
Although they require an atmosphere to breathe, Unggoy are capable of surviving in the vacuum of space without sealed, full-body gear. However, they must employ sealed face masks in order to breathe, as well as presumably to protect their facial tissues.
To humans, Unggoy are known to have a distinct smell of vomit, or manure, associated with their presence.
Although other species generally regard the Unggoy as a dim-witted race, many have proven to be very intelligent, resourceful, and knowledgeable. Indeed, the general perception of the Unggoy being inherently unintelligent is almost certainly a result of their poor education and training within the Covenant. Unggoy are one of the most gregarious and sociable of the Covenant races and possess a very strong pack mentality, often associating with each other in groups. This numerical superiority and pack mentality allows for their sense of cultural identity to remain, despite a number of hardships, including their extreme subservience to the other races of the Covenant, as well as the dark time following reintroduction after the activation of the Halo Array.
Unggoy develop sensory-motor integration relatively rapidly, and possess unburdened neural pathways which allow them to absorb knowledge more freely compared to the other Covenant species. As such, they were often tasked by the Covenant with monitoring space for traces of human communication. In addition, many Unggoy have developed a clear understanding of two or even three human languages. This advantage serves as a river of confidence in times of great stress for them.
On the battlefield, Unggoy are generally not very creative, although they are quite capable of handling weaponry and operating vehicles and machinery such as Ghosts and Shades.
Unggoy breed prodigiously, with large egg clutches and short childhood periods. Unggoy spend their childhood in a larval stage. Adulthood is reached between the ages of 5 and 8 years. This combined with the large number of young per clutch, which could range from 5 to 12 Unggoy, and rapid sensory-motor integration development was one of the primary reasons why the Covenant cleverly used the breeding habits of the Unggoy to their advantage in battle, deploying the Unggoy as cannon fodder—this would play a key-role in their war against humanity. Overpopulation is a serious problem and in non-war times, strict laws are placed on Unggoy breeding.
Unggoy do value their ties to their offspring, but are usually separated from their families at an early age by the requirements of military service to the Covenant and other groups they are part of. They resent this greatly, but because of their low social status, they are unable to muster any response.