Fleas of Madness

Nothing about these pests looks unusual. Each is a black speck, tinier than a rice grain, living in the hair or fur of mammals and drinking their blood. They leap onto anyone who brushes against an infested host and can wait several days without feeding in rugs and bedding for a new body to arrive. Compared to them, a common flea is practically a gift. They have no means of communication.

The bite itself barely matters: a faint sting and a small red bump, but no real damage. Every hour or part of an hour spent in an infested place, or near an infested creature, carries a 75% chance of 1d4 bites. Any single bite has a 25% chance of instantly producing an effect like hideous laughter, the 2nd-level wizard spell, or irresistible dance, the 8th-level one. A dispel magic ends those effects.

Worse, every bite also demands a save vs. poison. If any of them fails, insanity creeps over the victim during the next 1d4 days. An animal or semi-intelligent creature grows convinced it is some other beast it knows, or even a person, and may try to walk on its hind legs and imitate human habits. A human begins hallucinating: a dungeon passage might look like jungle, companions might appear as monsters, and things that are not there may seem perfectly real. The victim acts strangely and unpredictably. Once the madness has taken hold, further bites call for no more poison saves since it cannot get worse, but they can still trigger the laughter and dancing effects.

Magic can heal the madness: the wizard spells limited wish and wish, the priest spells heal, restoration, cure disease and heroes' feast, or the psionic science psychic surgery. A cure does not prevent a relapse if the victim is bitten again, so the only real fix is clearing out the infestation. Wizards can fumigate a building with stinking cloud, cloudkill or deathfog. Priests can protect a single person with repel insects or anti-vermin barrier, and psionicists can do the same with the inertial barrier devotion.

These fleas are found nowhere but the misty dread realm. They break out in a different spot each summer, swarm there for the season, and die off with the cold. Sometimes pets or vermin carry them indoors for the winter, so one house or village goes mad while the next stays untouched.

No one knows where they came from. Those of a scientific bent say they are plain fleas carrying a plain disease, and hope some herb or chemical will cure it. Others note that two of the effects mirror wizard spells and suspect sorcery: perhaps a wizard's curse spoiled a summon swarm, or an evil priest blended summon insects or insect plague with the madness spell mindshatter.