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.
When about three spawn, one will turn into a alpha, ( large and orange) which are the ones that drop the venom. WARNING: When they drop the venom, a bag will drop with the venom inside, it won’t go into your or your tames inventory!!! If ten spawn, a reaper will appear. Keep a light pet with you so they don’t overwhelm you. Light pets will burn them, doing major damage. That’s really all you need to know to fight them!