From Halopedia, the Halo wiki
A Kralidonk is a type of fauna catalogued by the Forerunners and preserved on the Ark. Described as "arachibians"[Note 1], they are hive-minded predators that travel and act in large swarms. From a distance, kralidonk swarms resemble little more than a shadow passing along the landscape, though they are capable of ripping apart dropships in an afternoon or reducing a Jiralhanae to a skeleton in seconds.
The kralidonk were one of many species known to the Forerunners, and preserved by them on the Ark during the Great Purification. As of 2559, kralidonk swarms were still alive on the Ark and inhabited the lake in the Chasm Lands Biome, where they had constructed an underwater city.
Anatomy and physiology
Kralidonk are small creatures and light in mass, capable of crawling up limbs to grapple with their prey. The creatures have tiny heads, allowing them to push between armour plates and use their sharp mouthparts to sever clean through circuits, undersuits and flesh. Even a single lone kralidonk was considered a threat to a Jiralhanae in power armor.
The kralidonk do have some level of intelligence; they are a hive-minded species and travel in vast swarms capable of eating their prey alive in seconds - or even eating through the armoured hull of a Eklon'Dal Workshop Lich dropship in hours. The kralidonk construct cities in their underwater habitats, and are known to decorate these cities with loot they find such as salvaged armour and equipment pieces or even retrieved shell casings. When the Clan of the Long Shields enagged a kralidonk swarm and fired upon those attempting to steal such technology from the crash site of Pegoras, the swarm was able to react quickly and resort to only stealing pieces of scorched flesh from the Lich's now-dead crew. Kralidonk in combat may also arrange ambushes, allowing them to get the drop on their victims in close-quarters.
List of appearances