Yes. They appear on new growth. A few varieties retain them.

Christopher

Oh, I didn't know if they'd turn into flowers or something.

Cooper,

They wouldn't, but the vestigial leaves help the plant grow. The flowers come out of a different formation.

They have appeared on my opuntia new growth but die as the pad matures.
I know the austrocylindropuntia will keep its leaves and mine has just lost them as it's becoming cold.

Wow I checked out that Austrocylindropuntia- very cool I want one! Are they pretty hard to find in stores?

I'm in the UK, I got mine online in a collection of cacti. It does look good when it starts to grow butthw 'spines' are like very thick hair that will stick in you and stay there it's annoying!

That happens a lot with Opuntia- the little ones look all fuzzy and friendly then you get little needles in your fingers. Washing with soap and water usually does the trick.

Really? Am there for hourstrying to remove the spines with tweezers lol

Well the tiny ones you can just wash and scrub off.