I always end up killing frog babies by stranding them on roofs.... Behind blocked mine shifts... cutting down their treehouse... digging holes under them... collapsing floors... deconstructing bridges... first attacked by invading armies... locked outside during a megabeast/titan/dragon attack... generally exterminator and frog babies are the worst... they are so antisocial they end up where no one is and then you can't get them to move.
I've been playing some Succubus recently and have been having these issues as well, and I think I have an idea for them. I don't know DF hack, so I'm not sure if it is possible, but a 'Summon Spirit of Corruption' interaction at the summoning portal might do the trick. For the cost of a prepared meal, a random sentient non-Succubus baby or child on the map is transformed into tame adult non-sentient evil biome creature.
Another idea might be a 'Corrupt Restless Spirit' option at the Den of Inequity that turns a non-Succubus ghost on the map into something useful. Perhaps even a 'Combine Ghosts into Horrible Fell Spirit' that can serve as an alternate means of summoning a demon.
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On another note, I've been wanting to practice modding raws, and would love to contribute a bit over winter break. I'm open to suggestions for where I can help, but I was thinking of making Succubus castes for the fortress defense races; It would be easy enough for my first experimentation with the raws, as I'd have the castes you made and the original fortress defense races to use as a baseline.