I'm looking to devise an extraterrestrial parasitic organism that perpetuates itself by infecting entire stellar biospheres before moving on to colonize other inhabited star systems. This organism would be a very well adapted interstellar apex predator.
The concept is inspired by the Halo franchise's "Flood" species, but is intended to be much more fleshed out and within the realm of hard science fiction.
The parasite seizes control of the body of a host and utilizes every means and resource at its disposal to make the host a maximally-efficient vector for transmitting the pathogen to other potential hosts. This includes hijacking the host's nervous system to influence its behaviors (similar to what Cordyceps does), and converting the host's natural cells into the parasite's dynamic cells, giving the parasite the ability to cause the host to undergo massive anatomical/physiological transformations (sometimes very rapidly).
Hosts will be able to communicate using pheromones to coordinate group action and inform the parasite how to behave at different stages of the epidemic (e.g.: not to make itself too obvious at first until it has a strong foothold over the population, etc.), making them an effective swarm intelligence.
Eventually, when enough of a sentient population has been subjugated, many sentient hosts should converge to form a gestalt, group mind "brain", capable of applying higher reasoning and tactics to its cause of infecting as much as possible with maximum efficiency. At this point, the groupmind and all of the hosts within its range effectively become a superorganism. The groupmind would broadcast its directions to the infected population telepathically (using the EM method depicted on this thread, which brings me to question #3 in my list below).
When everything in the groupmind's reach (typically a star system) has been completely subjugated, assuming the groupmind has achieved sapience and has the resources of a fallen interplanetary civilization at its disposal, it would then devise a way to colonize as many other star systems as possible (with priority on the star systems that seem likely to have life, particularly sapient life).
I'm looking to maximize the virulence of the parasite, as well as the plausibility of the concept.
It must be able to exist within a hard science fiction setting: no FTL travel, humanity is confined to the Solar System (and for the most part, just Earth). I've considered the fact that the lack of FTL travel is a hindrance on the parasite's ability to jump between star systems (given that it can't just hitch a ride on an FTL ship), but it could hitch a ride on a sub-light speed ship.
My questions/problems are:
- What should the infectious agent be (e.g.: bacteria, fungus, virus)? Would the copious amount of DNA that such a well-adapted creature would require fit inside of the infectious agent?
- Flesh out the mechanisms behind the parasite's functions, including its neurological hijacking ability and its ability to rapidly transform a hosts body. Point out any specific obstacles and/or physical impossibilities with these processes you can identify.
- Would the parasite be able to acquire and integrate enough metal into its host's nervous systems (or even the nervous systems of only certain hosts, such as locational nodes) to facilitate telepathy? If not, are there any other ways to create centralized groupmind? If not, are there alternatives to this groupmind?
- How should the groupmind's colonization protocol work to maximize the likelihood of landing in a star system inhabited by a sapient, spacefaring civilization that its offspring will then be able to launch its own colonization effort from?
- Any issues with what I've described above?
- How might such a species evolve?