Lusus naturaeSburb Logo, also known as custodians (although custodian appears to refer to the roleSburb Logo while lusus refers to the creatures themselves), is the Hivebent equivalent to a Guardian. They look after the young trolls while the adults besiege other star systems in the name of Alternian glory. It is also observed that a trolls' gender matches that of their lusus.
In Latin, the plural of "lusus" is "lusūs". In English, "lusus", "lususes", "lusii" and "lusi" have all been used, with lusii being the most common (and also used in the title of a song ♫ from the Alternia album).
Trolls and their custodians have a peculiar arrangement of codependency. The lusus behaves as a lifelong bodyguard, caretaker, and visceral sort of mentor, while the young troll must learn to function as a sort of zookeeper. The death of a lusus results in the young troll getting culled.Sburb Logo They are almost always seen in some variation of Hero Mode, especially those of the Sea Dwellers.
Lusii choose the troll they will raise. Scent plays a role in the selection process.Sburb Logo
They are horrifying beasts found in the ceremonial brooding caverns once the young trolls have completed their many dangerous trials. A troll's lusus is dependent on their blood color, as seen here and there, and possibly by gender as well. Together the young troll and custodian surface from the subterranean vaults and build a new hive using carpenter droids.
It was revealed that all but one of the trolls' lusii would die (Aradia's lusus being already dead) due to either the effects of the Mobius Double Reacharound Virus or the game itself, and would then be used to prototype their respective troll's Kernelsprite. They were all prototyped before entering the medium, so the troll's enemies have all their characteristics. Through these prototypings, the lusii gained the ability to talk with their charges for the first time.
The lususprites seem to have all died, either through the end of the game itself or because of Jack Noir.
Openbound seems to imply that each pre-scratch troll has the same Lusus species as a caretaker as their post-scratch counterpart, with the possible exception of Meenah. The same may be true for all ancestors, as at least Mindfang and Redglare had the same type of Lusus as their descendants. This would again have at least two exceptions, because the Sufferer was raised by the Dolorosa and the Handmaid was raised by Doc Scratch, thus neither had a lusus.
Eridan hunts a flying Whale lusus, belonging to an unknown, indigo-blooded troll.