Do you know if Sempervivum can suffer from this little critter?
My mint had a few on there and I was worried they'd spread!

Yes, they can. And they can spread. I have yet to have any aphids on my Semps but I have a number of other insects out there that eat aphids. Some of these are brachnid wasps, ladybugs, praying mantises, and damselflies.

I have ladybugs hybernate in my bathroom every year! I will have to put them onto my plants in spring teehee :D

Yes, put those little wonders to work! In our last house, I had them hibernate in the window and walls of the stairwell to the basement. Whenever it got warm, they started moving around everywhere. Lots of them!

Finally, someone who knows my pain, ladybirds everywhere in my bathroom! haha :D

I understand that, believe me. Hundreds of them!! I never had that before inside of a house until our last home. Wow, were they ever busy when the weather warmed. And if you try to handle them, they do emit an odor. PU!