Faced with the reality of something so viscerally terrifying as the Felos Spider, arachnophobia goes from being an irrational fear to being a necessary survival instinct.
Believed to have been first sighted in South America’s Amazon rainforest, where they preyed almost exclusively on uakari monkeys, Felos Spiders have since taken advantage of human technology and infrastructure to spread opportunistically - although fortunately in isolated incidents - around the world. They are named for an abbreviation of the pluralised ‘felo-de-se’, a Latin legal term which translates to ‘a felon to himself’ in English. The phrase, referring to those unfortunate enough to take their own lives under a legal system where the act confers criminal culpability or those who die recklessly in the execution of a crime, became attached to the species as a result of their self-destructive and gruesome parasitic reproductive cycle.
Reproducing asexually, Felos Spiders undergo a method of propagation which is highly atypical in multicellular animals and is usually the preserve of algae, ferns and fungi; the production and expulsion of statismospores. Lacking spinnerets, along with all sexual organs and associated apparatus, the abdomen of Felos Spiders instead house a gleba, a tightly packed mass of fleshy spores, pressed up against their exoskeleton to be released when it is broken, breached or pierced. Sightless, the spiders are incredibly sensitive to vibrations and use this faculty to locate suitably large prey - always primates in their natural habitats - relying on said prey to crush or otherwise kill them in order to force the release and spread of their spores.
The necessity of a deliberate and destructive death has led the Felos Spider down a somewhat paradoxical evolutionary path; that of a dangerous predator which must appear like particularly hapless prey. Though their eyeless bodies are small and predominantly an unassuming brown colour, adult Felos Spiders have a ragged ultramarine circle on their cephalothorax after their final moulting. This bright marking, along with an instinct to dash towards and even pursue animals that might kill them, make them an extremely noticeable, eye-catching presence. When hunting the uakari monkeys they essentially goad their prey into smashing them or, if the uakari is too young to know better, eating them. In humans they might have found an even more perfect prey, unknowingly playing on arachnophobia and the violent panic it can cause to achieve their biological endgame.
The plum of spores released when a Felos Spider is crushed is almost explosive in its violence, creating a fine spread up to six feet in all directions from the exposed gleba. Unlike most spores, which can carry workable genetic material for long periods of time, those released when the Felos Spiders are crushed are only viable for an incredibly brief period - a matter of seconds at most - before becoming inert. After this point they are indistinguishable from motes of soot or dust, both to the eye and to more intensive and invasive analysis. For some though this limitation is not enough to be spared: If the living spores are inhaled, ingested or absorbed through the membrane of the eyes then it is already too late.
On those rare occasions where a medical intervention has been possible, both broad spectrum and specific antiparasitics have been exhausted as potential salves. Full-body irradiation has been posited as a potential cure for the infestation - albeit only being practical during a very small window in the hours immediately following exposure - but this would also destroy a person’s immune system and would not repair any damage already done. Worse still, if the spores survived this treatment it might lead to more pronounced or severe physical changes; a lack of antibodies and white blood cells potentially allowing a hardier, healthier or larger number of Felos Spiders to be born from a weakened host.
Where other spores contain the genetic material to allow a species to regrow, to spread anew from a single source, those released by the Felos Spider are also mutagenic; changing the host organism into the perfect incubator for a new crop of the spiders. The change is slow in the beginning; more acute in its psychological effects than the physical mutations that follow. Over the course of a few days the host becomes emotionally withdrawn, their ability to exhibit or understand empathy disappearing as the people in their lives recoil in confusion at the way the person they knew is changing. If the host feels challenged, threatened with a medical or psychological intervention against their will, they may disappear, seeking solitude and sanctuary wherever they can.
If they feel trapped, these hosts have been known to become violent in their attempts to escape, sometimes taking the lives of loved ones without a glimmer of mercy or any sense or semblance of the person that they had been even a few days prior. Once they have isolated themselves, whether peacefully or not, hosts develop severe agoraphobia and a sensitivity to light, the spurs to finding or creating some kind of small, dark enclosed space where they can gestate their parasites in peace, away from any obstacle or opposition. There, alone in the darkness and terrified of coming back out into the light, aspects of a host’s biology begin to change to accommodate the young Felos Spiders growing throughout their bodies.
Over the course of a week, two at most, they are broken and reforged; the process doubtless unspeakable in its agonies, even if they had anyone to tell. Their skin becomes as thin and brittle as ancient paper, tearing whenever they move, and their closed eyelids are fused by eyeballs which slowly liquefy into a leaking sealant. Every spore in their body begins to swell, growing to the size of a marble as the Felos Spiders prepare to hatch. These newly-formed eggs choke off blood to the areas around them, wreaking havoc as the nearby damaged tissue necrotises, before growing tendrils which anchor themselves to the nearest bone. These tendrils then push against the bone, a rigid spindle which drives the eggs closer and closer to the skin until, finally, they tear through and hatch.
Carnivorous carrion feeders from birth to maturity, the newly-hatched Felos Spiders gorge themselves on their former host until they reach their adult stage and, abandoning the dead or dying and partially ingested host, go to find victims of their own. If were not for the fact that the only primates seem to be able to host the spores, that only healthy hosts survive an infestation long enough to allow for new Felos Spiders to be born, and that their markings and behaviours make them easy prey for predators unsusceptible to their spores, then they might represent an existential threat. Instead the ruined remains they leave in their wake, a broken body surrounded by the husks of their younger selves, might merely be among the most terrible things it is possible to witness.