I think these guys are test tube babies. Anubis has a facility somewhere where he simply clones them in tanks and "activates" them when he needs to. Both the host and symbiote are both likely clones, since both are genetically manipulated.
I don't like how indestructable these things are. It's too campy. What is the SGC to do? I guess we'll have to wait and see. (for more info on my opinion on this issue see my post in the Evolution Part 1 thread in the Season 7 section)