Nexifera are, basically infested dropbearspiders.
Why would you want to capture such accursed evil? Because there’s a floof, and Son sometimes wants them.
How do you find a Nexifera, good question, you can tell they’re there by the green corrosively looking slime puddle on the ground directly beneath it. Usually surrounded by 2-3 Cryptilexi of various rarities.
The most common spot, is the neon pink colored cave to the north. (Which I must warn you, extended stay in that cave may cause nausea and headaches. I recommended turning the bloom down and taking breaks if you do suffer from that.)
The easiest way to capture them would be shooting an Ivara arrow straight up from the soylent green puddle and they’ll drop down. Note that Nexiferi wake up VERY quickly. Suggestion would be sleeping all the free tags Cryptilexi at the bottom before firing a sleep arrow straight up.
How do you capture them without Ivara? You shoot them with the tranq as they’re reeling back up.
The rarities of Nexiferi suggest they will attack you should you be standing visibly under them. The rarest Scarlet Nexifera, the one time I did come across it, 2 of them dropped down at once. I’m unable to confirm if that’s a constant yet.
Good Luck and Good Hunting Tenno.