Oakmoss was a coastal fishing village near a small inland lake on the Sword Coast. A stretch of cliffs a short walk from the village were riddled with small, shallow caves. Some believe that the small creatures were summoned from another plane of existence and unleashed upon the people of the village. Others suggest that they were mutated by some kind of alchemical mutagen or arcane potion. Either way, the parasites fell on the village in a swarm from the caves, first drinking the villagers dry of their blood and then taking possession on their lifeless bodies.
The Waterdeep Navy dealt with Oakmoss by burning it to the ground, including every remaining villager. The whole area was left lifeless, with everything of value gone and no one to call it a village anymore. But vermin have a way of surviving, and surivive they did.
Oakmoss Parasites, also called Corpse Fleas, are small flightless insects. As parasites of mammals and birds, they live by consuming the blood of their hosts. Adults are up to about 3 mm long and usually brown. Bodies flattened sideways enable them to move through their host’s fur or feathers; strong claws prevent them from being dislodged. They lack wings, and have mouthparts adapted for piercing skin and sucking blood and hind legs adapted for jumping. The latter enable them to leap a distance of some 50 times their body length, a feat second only to jumps made by froghoppers. Larvae are worm-like with no limbs; they have chewing mouthparts and feed on organic debris.
However, the Corpse Flea is most feared for its interaction with corpses. It has developed its necromanical desires into a way of life, using corpses to propagate itself. Whereas a fly will merely implant eggs into a corpse and leave, letting its offspring use the corpse as nourishment, this creature instead crawls entirely inside a corpse then uses it to walk it around, spreading small nodules shaped like spikes and akin to seeds as it walks. A clear ichor that serves to accelerate the growth of its nodules accompanies the spikes. This ichor often seeps from the orifices of the host.
When a Corpse Flea traveling inside a host encounters another dead body, it “spits” one of its spikes into the body. The spike injects fluid into the corpse, and the spike itself slowly burrows into the body, toward the heart, then grows. Within two days, a new parasite fills the chest of the corpse, animates the body, and walks around searching for dead bodies on its own.
These creatures do not seek to kill living creatures and try to avoid them. However, they are drawn to blood and, like vultures, seek out living things they sense may die. If attacked, they won’t hesitate to defend themselves, spitting spikes at opponents.
The Oakmoss Parasite can sustain a corpse for up to a month. While its fluid prevents the decay of muscle and connective tissue, the creature must eat. The corpse itself is the most convenient source of food, so it nibbles slowly on the inner flesh. Once the body has ceased to be of use, the parasite crawls out through the most accessible opening and inches away, looking for other bodies. Naturally, the beasts are attracted to battlefields and the enormous pickings to be found there. However, the Corpse Flea is keen to pick bodies that are intact. Any gross openings in the skin will allow too much of its fluid to leak out. Therefore, it is more likely to pick a body that has died from blunt trauma than from, say, being hacked to death. It prefers animals and people that have died from sickness. If it cannot find a corpse, it chooses some place to wait until it smells a corpse. It prefers moist hiding places; ideal locations include coastal caves, since they’re dark and wet, and stagnant lakes. During the night, it may sometimes roam the countryside if it is desperate enough.