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.
Make sure if you have a blue base that you have lots of light in it otherwise they will spawn in your base :/...to kill them all you need is a light pet and something strong like a drake, crab, reaper, spino, mega ect. Make sure your light pet is turned off so they spawn and then run around making more spawn then turn your light pet on and go ham...this is an effective way to get nameless venom as light will nerf them a lot and stop them from spawning :) enjoy.
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.
Just from my experience. Bring a ravaged level 100+ with good melee and health and these things are a piece of cake. My friend and I went down with high level ravages and no light pets and we shredded lots of nameless. Just bring the light pet if you want to avoid them along with high level ravagers.
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.