For possession/merge type spirits, like Bugs, I imagine that they don't do much. Keep in mind that the spirit takes over completely, but if it's a good merge it can access the hosts memories. So at worst, it just means if CFD messes with the memories of the host, the bug can access those memories. Not that it will make much difference one way or another to the bug.
Hrmm... Maybe Bugs and Vampires and Ghouls will be the savior of humanity from CFD?
Hehe... Hehehehe... I like that.
Bull