They come out of the ground in groups and when exposed to bulldog light they catch fire and burrow back into the ground.
Sometimes they can be damaged if they burrow into a protruding boulder.
It seems like they spawn more nameless whenever they unearth themselves. They are easiest when you have enough dps to kill them before they burrow. Attack them with friends if possible.
Appear in the blue and red areas and the surface. Normally they don’t spawn onto you just because you have no charge, they seem to spawn around like normal dinos and are drawn out when you have no charge. This means you CAN clear areas of them for a while at least if you kill them before too many spawn from alphas. Have a light pet with you but have it off to draw them out, then when they emerge turn it on and use a strong mount to kill them off with ease, preferrably the crab. They also seem to take crush damage from big dinos walking over them even when they’re underground (though this may have been fixed). Plant Z fruit can force them underground which could save you in a pinch.
If you plan on building in the bio luminescent area be sure to have plant z on the outside of your base. Preferably out of reach of the nameless. Growing these will keep them away from your base, thus preventing a reaper king from knocking on your front door.