I still find it odd that some invertebrates are welcome and even coerced to reproduce, while others are exterminated. It's analogous to a similar debate I often have with my wife - what constitutes a weed? Many "weeds" that she pulls from her garden and flower beds are just as aesthetically pleasing as the "non-weeds."
If anyone else has a hydra outbreak, bag some up and ship them my way.... I find them extremely interesting.