Unlike the common type who just say good things when they first join the group and disappear after, this type is a bit more annoying.
The part of not contributing is still the same just that these "evolved" species keeps bugging you by asking, "when are we going to gather and do the assignment?". After gathering, they just sit there and rot away.
In the end, leeches are leeches. They get on your nerves whatever type they are.