Well, I finished compiling my list of Flood posts, it's not in any particular order mind you [actually everything's kinda jumbled aboot], but yeh might be in for a good read.
Insect anatomy doesn't really seem to allow infection. With what we know about Flood, the infection process would fail.
In my view, 'sufficient biomass' means the host is not big enough to contain a Flood infection form within it.
Meaning something too small for an infection form to aquire, is infected in a different manner.
Calcium is a neccessary ingredient in the Human nervous system. It is what fires our synapses. Perhaps the Flood don't need it for their cell bodies, but actually to complete a connection between the Flood parasite and Host.
I've also just read in a recent Scientific America magazine about virus' and whether they are truly alive.
Remarkably, they describe how a virus can "come back to life" or bring it's host back to life. Essentially, when a cell loses it's DNA, it's done for. Cell processes can no longer continue, The Endoplasmic Reticulum stops making proteins, the Golgi Body stops packaging things, and so on.
However, a virus can insert its own DNA into this 'dead' cell, and all the machinery will start up and run again. Meaning a virus doesn't need a living host.
A virus also does this to itself in a different way: If any DNA is remaining, it can reassemble from all its broken parts, and voila, your Virus is back up and functioning again.
Now this has got me thinking about what the Flood can infect.
It's clear that Flood can infect 'dead' bodies before they decompose. But what makes a living host an actual moving Flood Form? I think it would be the brain.
How fast do the synapses in a brain break down after death? (For instance if they stopped getting O2) If we can answer this, we will know how long a body can be 'dead' before it is no longer a viable form for movement.
You see, the Flood are a completely alien lifeform, there is no way in hell they'd know how to control another alien's body. Unless they infect the victim's brain and, more importantly, it's movement control center. In Humans this is the Cerebellum.
So, Flood which infect a dead body will be pretty much benign. They will have no ability to move the body, and will only be able to convert it into a Flood mass. These masses probably grow into incubators for Infection Forms (Not like the ones that walk around.)
Vectors that are infected while alive however, are much more dangerous. The Flood form now has the host's knowledge, and can move itself around. This allows it to incapacitate other vectors and consume them as well.
Now this brings me to where the Flood may have come from.
It's unlikely the Flood were the only thing to evolve on their planet. So, logically, there were, (or are) other things living on said planet. Things that would likely have a defense to combat the Flood.
Or possibly... Flood are only lethal to things not from their planet - everything there has grown a biological immunity to it.
The Flood would be like scavangers on the planet. Dead bodies would no longer have a working defense mechanism, and thus were infected by the Flood. However, these bodies would remain benign, becuase the Flood virus would not know how to control its host. (The brain has died. Hopefully.)
So, we've got a nice balance on this world. The Flood can't just infect the entire planet, and destroy all other life. Instead, they act as garbage disposal, removing unwanted baggage (dead bodies) from the area. Of course, some other animal would find these Flood masses a tasty snack and eat it. Keeping Flood numbers low, and recycling the dead matter back into the ecosystem.
Now, lets introduce something new: Forerunners. They come from a different planet, have no immunity to the Flood, and decide to take a nice exploratory survey of this beautiful new world they've found.
Upon breathing the planets atmosphere, the Forerunners also inhale Flood spores. These spores release the virus through the respiratory organs into the circulatory system. Soon, these Forerunner pioneers become deadly Flood combat forms capable of higher thought. Suddenly the Flood are no longer a scavenger cleaning dead bodies off the floor. They are a thinking sentient lifeform. (of Doom!)
The Flood would realize (because its sentient now) that there are other worlds, planets, Forerunners, to infest. The Forerunner ship leaves, carrying a deadly package of Flood death.
What happens next is more speculation: Perhaps the Forerunners destroy the Flood homeworld, not realizing the consequences of this. Thus destroying any way they have of creating a cure, and dooming every race in the universe to a terrible, horrific, undeath.
But that's not the point. It needs the information in the brain. To control the host. After it has 'downloaded' the information, then the brain is no longer needed.
No, no. What I'm saying is that if the host's brain is dead. (Which Jenkins' wasn't.) The Flood cannot control it at all.
The neurons in the brain have decayed to the point where they are unusable by the Flood. Thus, that body just turns into a Flood Mass. Used for whatever purposes Flood Masses are used for.
If the Brain is still working, the Flood will sift through the information, and use the current Nervous System to control the host body.
Think of it this way: If you were suddenly in the body of an Elite, would you be able to move it's seperatable jaw? Humans don't have a seperatable jaw, nothing in our brain would have information about how to control a jaw that splits in half.
For all the adaptability the Flood have in them. There's no way they're going to know how to control all aliens, right off the bat. Not to mention the untold number of hormones, and enzymes, and other such things that need to be properly controlled. (Which are probably replaced, eventually, by the Flood Virus with its own systems.) All the information it requires for bodily functions can be found in the Brain and Spine. If those are gone, that information goes with it.
Hmm... ok, lets review the information you've brought forth:
1.)The Human host can regain control of the body if the Flood Infection Form lets it.
2.)The Flood tap into the Spinal cord, and block transmissions coming from the brain... Which would be the interneurons. I think.
To start off with. When the brain dies, there are no longer any working interneurons, a transmission cannot be sent or received by the Sensory, and Motor Neurons. Not to mention whatever the host has learned from childhood in regards to controlling the body are also lost.
So, in essence, a dead body can not be turned into a functioning Flood Combat/Worker/Incubator form or any other form with mobility, aside from the Rangers.
When a Ranger infects a human, it blocks the neural pathways in the spine. Then it likely sorts through vital information within the hosts' brain. Information like coordination, and movement. Once this is aquired, the Ranger can begin testing out all the muscles, and ligaments, to move things like the arm. This would be done through its tap in the spinal cord.
It may take a couple minutes for the Ranger to become used to it's new body, as all the new data has to be processed. Once this is done however, the Ranger now would have complete control of the body. Unless it removes its spinal tap, which is what happened in Jenkins.
To control its host, the Flood Ranger requires a center in the brain which controls movement. Humans have the Cerebellum.
A Flood Ranger has tentacles as it's natural limbs. Humans don't have tentacles, and the information for moving a Human arm is going to need to come from the host itself. The Flood Ranger is not going to know this stuff on its own.
If you could imagine trying to move a tentacle instead of your arm, you would have to figure out how to bend it, what it's maximum mobility is, and so on. You cannot just 'know' how to work something like that.
I'm saying the Flood cannot learn this information by themselves from a dead body, rather they require a living host, with a coordination center in the brain that allows them to steal said information so that they may move the host.
Not to mention that in the Oracle, those bodies lying around in that room are already infected by the Flood. There is likely a memory storage organ that was created by the original infection form, which allows other Rangers to take control of the body without accessing the host's brain.
How long does it take a baby to learn how to move effectively? How much longer after that, before said child could move like an olympic athelete.
Even if the Flood could learn how to control a body, it would take years for it to be effective.
Once a Flood infects someone, I'd theorize that the current nervous systems are replaced by something the Flood prefers.
Gravemind is not a seperate being, like a queen. Gravemind is the collection of all Flood minds.
Everybody keeps talking about Gravemind like it is the overmind of the Flood. Gravemind is not. Gravemind is all the Flood thinking in concert together.
So, while doing some studying on the human nervous system I came upon the fact that in the Axon bulb are Calcium Ions. This pertains to the fact that Flood need a calcium supply and a nervous system to properly use a host.
Perhaps the Calcium and Nervous system go hand in hand, thus it's possible that the molecular makeup of anything the flood infect have calcium present in their nervous system.
Just some more information on Calcium:
A 60kg (135lb.) person would have around 1150 grams of calcium present in the body.
This gives us an approximation of how much Calcium the flood need for infection: 1.5kg (2.5lbs.) approx.
Here's an explanation of how calcium works in the nervous system:
When a nerve impulse reaches the axon bulb, gated channels for calcium ions open, and calcium enters. This rise in Ca2+ causes synaptic vesicles containing neurotransmitters to merge with the presynaptic membrane.
This essentially results in the nerve impulse continuing through to the next neuron.
So, we've narrowed down what "Sufficient Biomass" the flood may actually need.
Of course, it's still possible for flood to infect something with less calcium, as we don't know what the minimum requirement is yet.
I highly doubt you even can be immune to flood infection. The closest thing that comes to it would be overpowering the flood's mind. (Which Jenkins did somewhat.)
Remember, an infection form drills into your chest cavity, taps into your nervous system, and releases chemicals to begin changing your biochemistry.
A couple billion white blood cells, Macrophages, Antibodies, and the like are not likely to be very effective agianst such an invasion.
Not to mention that the infection form likely destroys most of your immune system' defenses; Spleen, Liver, a lot of Marrow, your Thymus, etc.
I've gotten a distinct feeling that the flood are treated more like a Biohazard in their containment, then as a sentient lifeform.
In "Arbiter" as you take a joyfilled elevator ride down, the machine you happen to be on is picking up canisters. If you happen to break open a canister, infection forms appear.
If you look at dangerous diseases on earth, we also keep them in cold storage for study and containment, should they ever happen to appear again...
Although the Flood can be argued to have a difficult time in cold weather, I would argue that the fact they are a very versatile, and adaptable, parasitic lifeform, that they are by definition, almost immune to weather conditions.
Instead of looking at wether the weather effects the Flood, we should look at what is not the Flood that is effected by the weather.
How many animals live in a square kilometre of rainforest? How many live in a square kilometre of arctic ice?
The Sentinals destroy any life that grows too close to the Flood, and to aid them further, they lower the temperature to prevent things from growing back as quickly. Making it easier to find and remove potential vectors.
The only thing not corresponding to this is the level "343 Guilty Spark" Which is located in a swamp. (All other situations however, follow the basic 'cold' setup.)
Whew! Finished a'ready are you? Well how's about you add to what I've got here with corrections, and your own theories. I like theories.