A single Kryll consists of a worm-like body, a head with a blunt muzzle and pale yellow eyes. Just behind the head are six limbs that encircle the body with a thin membrane on each of them, serving as wings. The mouth of the Kryll is filled with many razor-sharp fangs. Being subterranean creatures by nature, Kryll are extremely photo-sensitive and will be blinded by sunlight. Concentrated ultraviolet light will cause Kryll to burst into flames.
Kryll live and hunt in complete darkness and always travel in vast swarms. Sleeping within the Hollow by day, they would emerge at night to hunt for food. They would eat just about anything that left the light, including humans, swarming in countless numbers over individual prey and rapidly gnawing them down until nothing was left, not even bone. Even the Locust were vulnerable to the Kryll's limitless appetites, though were often ignored when there was an abundance of humans to feed on.
During the Locust War, the Locust developed their own ways of weaponizing the Kryll. The Theron Guard sometimes used specialized grenades that could attract swarms of Kryll to a specific target which the creatures would then tear to shreds. General RAAM also displayed the uncanny ability to manipulate Kryll directly, something that no other Locust has ever done. When entering battle, RAAM would summon a swarm of Kryll and direct it to attack Gears or even use them to shield himself from attacks.
Following the Lightmass Offensive at the end of Gears of War 1, the entire Kryll species seems to have become extinct. The Lightmass Bomb that was launched into the Hollows devastated their breeding grounds, leading to the entire race being wiped out. Since then, Gears and Stranded have been able to go out after dark without the fear of being eaten alive.