When the eggs make contact with your skin, they hatch and burrow into your flesh, like blowflies or lice. While you sleep, they’ll crawl out and migrate across your body in the fashion of bedbugs, seeking the best hiding and feeding spots. Ideal for them is access to your digestive system.
As they grow, each can split apart to multiply, each asexual generation enhancing the odds that a questing worm arrives at its goal — as well as making the infestation that much harder to permanently root out.
Still, this presents the first major fork in this branching evolution.
What happens if the larvae achieve their goal: migrating to the digestive system? Or better yet, the eggs were lucky enough to hatch there in the first place — perhaps because they’d laced the hosts food?
They reached the intestines and grow fat there, unconstrained by the need to move or hide. Here there’s much less work to do — now it can simply gorge itself on the hosts’ food (a theft which encourges the host to eat more and more) while it only grows longer and thicker. Eventually, there are enough larvae crowding their guts to bulge the stomach. But that doesn’t mean the growth will stop.
Unchecked, the larvae will continue replicating even after the host loses strength or ability or willingness to keep feeding. Even after no more space remains in the gut, they can simply burst outward and infest the rest of the internal organs. As you might imagine, no host will survive long with a chest so full of hungry spawn unleashed; maggotslime drowns their lungs and their ribs burst while the heart is devoured.
This is the the natural, ideal process of infestion — the parasitoid lifecycle.
A special note is to be made of alternatives to the gut. It’s the ideal, but it’s not the only place the maggots can take up residence. The reproductive system can provide refuge — mainly in cases where the host has a womb. Advanced manipulation of hormones may even persuade the body to direct nutrients to the passenger of its own accord.
This is not the only possible outcome of the maggots arriving in the digestive system, but before explaining the alternative, it’s illustrative to examine what happens if they cannot achieve this.
So next let’s suppose they never make it to the intestines. This means they must survive by subtly draining blood and fat deposits. What exactly happens next depends on the host’s response.
Most obviously, one may notice the bites, the growing weakness and fatigue, the inflammed sickness of an immune system expelling invaders. If one examines oneself carefully, one will notice the wounds, the blisters — one might even catch a worm in the midst of its wriggle-scurry across an exposed stretch of skin, darting to the cover of a patch of hair.
If the host scratches at the wounds, squishing or tearing out the larvae, and wipes themselves down, then one creates selection pressure for larvae to adapt and hide themselves from notice.
Thus, energy will be diverted from just feeding on the host to camouflage. This already happens on a chemical level — sucking up genes and hormones to imitate the chemical signature of one’s biology and hide from the immune system’s notice — and eventually it also happens on a physiological level.
At an extreme, the worms will eat the host’s muscles, biting into their attachment sites with teeth and tail-spikes, or cutting open one’s vessels and routing one’s blood through themselves. Bit by bit, one’s flesh stops being one’s own. It still responds to one’s nerve signals — for now, so long as that aligns with its own agenda.
This is the fusomorphic lifecycle.
But again, this is an adaptation — it cannot happen if there’s no need for it to happen. You may have seen photos of people with necrotic wounds that have decayed to the point of having maggots visible in their cavities. And of course, those awareness campaigns telling people to check for suspicious lumps wouldn’t be necessary if everyone noticed these things. It is entirely possible, given the right host in the wrong circumstances, for the infestation to develop to an advanced stage essentially untreated.
Thus, the maggots may gather themselves into a tumor-nest and extract nutrients with little if any pretense of mutualism.
Now, easily this scenario mirrors one of the cases we’ll discuss later on, so what’s essential for a unique outcome here is that eventually, this affliction becomes taxing enough that either the host is forced to finally seek some treatment for it, or the host begins to outright fail in gathering sufficient nutrients for the parasite.
Importantly, this all must happen before the larvae have finished gathering the resources needed for their pupal metamorphosis.
As a result, the parasite is finally forced to divert resources from extraction and growth toward reinvestment in the survival of its host. This can mean synthesizing hormones like dopamine and adrenaline to motivate behavior, and it can mean repairing atrophied muscles and necrotic flesh with the same techniques of replacement-imitation outlined in the fusomorphic lifecycle.
But this outcome is a bit different. What distinguishes this is that here, the parasite isn’t hiding, nor is it integrating into the hosts’ biology. Rather, it is colonizing it. The parasite has centralized itself into the tumor nest, and it only extends larva-tendrils into the the limbs or hormone-signals into the bloodstream as something more akin to puppetry.
So that’s a decent enough name for this: the quasicolonial lifecycle.
But remember that first fork in the road? We didn’t finish exploring the rest of it.
So, imagine the larvae had arrived in the digestive (or reproductive) systems by migration. This naturally implies that while some can live out the easy life in the guts, their sisters are still scraping by outside. What are they doing?
In most cases, the intestinal larvae will pump covert hormonal messages into the blood, coordinating the colonies elsewhere in the host. If there are larvae in the gut, these hormones will suppress the formation of any rival ‘tumor-nests’ — which are just pale imitation of the gut-palace, after all.
This means that remaining larvae will be directed toward fusomorphic behavior. This can easily transition toward quasicolonial or outright fusomorphic, especially if the environment demands parasitic adaptation to survive, or the host makes an effort to get rid of the infestation. (But I repeat myself.)
Still, unique behavior can emerge in cases where the host is accomodating and the environment fruitful. This mean balancing on a knife’s edge. The parasite must grow integrated enough into the hosts’ biology to discourage outright parasitoid consumption, yet not so intertwined as to advance to total assimilation. It remains a pampered guest — free to leave at its whim.
This is the ovipositional lifecycle.
Thus defined, these are the four major modes, but the nature of a such a flexible lifecycle is that possibilities still abound.
A fifth mode, subtlest of all, can be most clearly outlined now that the last three are defined. Quasicolonialism implies a certain dominance of the nervous system; fusomorphism implies a total conversation of all limbs and organs; oviposition implies ultimate independence from what the body provides.
If those absolutes are not achieved? If the parasite is limited by the host, if the transformation-conquest reaches a stalemate, if the larvae grow too used to the shelter and indulgence of the body? One could almost imagine it the transplant of a new organ, a xenograft. This is the endosymbiotic lifecycle.
We can continue: what happens if the host is lacking — in biomass or in knowledge — and the parasite would prefer a mulligan? Larvae simply infest flesh; should they be lucky, they can migrate to a new host. Luck, or cunning: a host could be molded into vector replete with larvae and manipulated into infesting others.
But if those victims remain in contact? Fusomorphsis is, at its core, the weaving of new anatomy — what might result from larvae able to freely slither and insinuate between many hosts? (It’s there in the name; fusomorphosis happens because the because the boundaries between organisms are so easily blurred.)
But we are getting ahead of ourselves.
Now that we’ve enumerated the different modes, let us finally finally illustrate the most important difference between them all. Recall how the parasites have been repeatedly referred to as larvae — one is left to wonder, then, about the chrysalis and emergence. Larva must eventually spin themselves a cocooon.
In the parasitoid lifecycle, the coccoon engulfs the entire corpse (or agonized corpse-to-be).
In the fusomorphic lifecycle, the cocoon engulfs the host (or perhaps only one colonized limb at a time).
In the quasicolonial lifecycle, the cocoon only engulfs the tumor-nest (an ideal time to remove it — thus the cocoon often attaches near vital organs).
In the oviposition lifecycle, the coccoon strains against the guts or womb, but is adapted for the host to lay it.
In short, the entiote is profoundly adaptive. The host may be its prey to be savored from without, or a mere nest to occupy then abandon, or an assimilated extension of itself, or its fertile breeding stock.