Are there any special conditions for encountering Lanius?

I have been playing a lot of FTL recently, all of sudden I'm drawn back into the game, and with a vengeance. Since I abandoned the game a long while ago, advanced edition was released, and so I'm playing with it enabled all the time now.

As far as I know, the advanced edition adds a whole new race - Lanius, though I wasn't reading up on them in the wiki on purpose to avoid spoilers. However, I can't find any "Lanius Secrors", "Lanius Homeworlds" or the like so far, and never heard of them in game. Am I just unlucky, or is there any special condition to finding them?