Now that they've come out I've tested them a few times to try and see how they're tamed.

You wanna grab a tame (I used gigas), preferably with good stats and/or one you don't mind losing - and bring it to wherever they spawn on the map you're using. You should go off and kill a Rhynio (any gender) on your own first, or with said tame so that you can harvest a pheromone from its corpse. Once you have that pheromone, feed it to the tame and then go and find another Rhynio (I believe only females can infest your tames, correct me if I'm wrong!) And aggro it to your tame while the pheromone is affecting it. Keep your tame on passive and let the Rhynio do it's thing! You'll have to shoot the Rhynio while it attacks your Dino, and get it below and certain threshold of health. It'll then perform an animation as if it is about to spit resin, but will do some sort of dive/corkscrew into the tame and voila! Your tame is now infested. Your tame will receive strange cravings while it incubates the baby Rhynio, and they're strange. It can be stuff like element it wants, ranging from consumables like battle tartare to even ammonite bile and achatina paste, all kinds strange things. Once the incubation timer goes down, your tame will die and out will hatch a juvy Rhynio! They won't aggro onto you when you hatch them (at least not in my experience) so super easy to just run up and claim them!

You also can't breed them, I don't think. Doesn't let me anyway, which isn't fun.

More Rhyniognatha Taming & KO Tips