Previously, passing in `fits:blue` would cause a crash, because
`species_name` part of the split would be `nil`, oops!
In this change, we use a regex for more explicitness about the pattern
we're trying to match. We'll also add more cases next! (You'll note the
error message mentions `fits:nostalgic-faerie-draik`, which isn't
actually possible yet, but will be!)