Undead Beard Fleas
Horrible little critters in that they love the greasy, wiry habitat of a surely dwarven beard. Undetectable by the untrained eye, they are never the less a bane to any dwarf and their master work of a beard.
Dwarves are known for their pride in their beards, growing them literally since birth. A dwarf born without a beard is a human, or so the joke states. They spend their entire life growing and grooming their beard to the right size and shape, some putting elaborate tokens in them to tell tales of their victories and great battles fought, and great foes vanquished. Being as surely as they are, and not the most hygienic, it is more often then not that they can attract certain vermin that will nest in their beards and cause inconveniences.
From fleas to ticks, and mites to worms and all other manner of crawling things that don't belong there can crawl in, breed, and even thrive in a healthy dwarven beard. (A recorded grumpy old sea faring dwarf was once seen with a crab living in his beard, to keep out the sea spirits he claimed.) Some are proud of it, but most take it for granted of having a healthy and proud beard and call for a local Poosker to rid them of their vermin. There is, unfortunately one form of vermin that every dwarf fears, and rightfully so.
Roughly a century ago, a particularly vile and malicious necromancer found a spot of trouble with a near by dwarven clan. The necromancer Mour Ngr Ymn was arrogant, even for his kind, laughing in the face of those he taunted and murdered for his studies. They particularly did not like his ravaging the countryside in search of bodies for his experiments, especially when the subjects he used were of their dwarven family. A short, but all out war was waged on his fortress, and while he was not killed, the dwarves left him in a heap of rubble that left him with only a few minions remaining. Unable to retrieve all of their fallen comrades, as some were eaten to nothing, and some blow into far to many pieces to carry, they left and returned home.
He plotted to take action for the dwarves destroying his work. Having worked with the dwarven dead, he knew of their particular malady when it came to beard bugs. By using the bodies of the fallen and their own infesting infestations, he created a most vile and horrible creature to combat them at their doorstep and in their homes. He created a mass of them, enough to crush a small child should they been placed in one large group, and sent them forth with a small group of his new undead dwarven minions. Knowing that they would be destroyed he was not concerned with making them powerful or augmenting them to wreck havoc. He brought them back and animated them for the sole purpose of being carriers of this new mass weapon.
They did their job, not infiltrating the dwarven cavernous cities, but transferring their precious weapon cargo to living dwarves. Soon after, those infected realized that their usual pain and irritation from their beard vermin was not normal. Those afflicted by these undead beard fleas, were experiencing symptoms of decay and rot. As if they were a form of death walking. The undead fleas do not kill, just saps the strength from their bodies.
While it is extremely easy to be rid of them, to shave the beard and burn the hair, most dwarves opt to be killed instead. Feeling to have ones beard cut is as close to a living death as they wish to have, they choose to go all the way.
While the dwarves have found a way to control them by using Beardspiders, it does not kill them. It simply keeps them at bay and slows down their breeding. Being extremely difficult to destroy outside of fire, the beardspiders eventually lose their battle, and more must be placed in the beard every few weeks or the undead fleas begin to multiply faster.
The purpose of these nasty creatures is not to annoy the infected dwarf, but to torture and eventually destroy them. Dwarves of all people understand the concept of a small thing being used to alter something far larger. Take a droplet of water that endlessly drips onto a cavern floor. Small at first, but eventually it wears down the stone and creates a hole that eventually can amass great depth. The undead beard fleas do the same thing. While infested into a dwarven beard they begin to feed on the dwarves life essence, unlike a normal flea that feeds off blood. It takes one feedings for one of these undead fleas to be able to reproduce others of their kind. This is why it is difficult to be rid of them.
While in adult form, the undead flea can in fact be destroyed by dipping the beard in holy water, or a possible exorcism Though most respectable priest would balk at wasting time and effort into ridding a dwarf of fleas, instead telling them to just shave their beard. Possibly different outlook for a dwarven priest. But after they lay their eggs, the life cycle of the flea changes. They are no longer simply undead, but half dead. The eggs are in a state of half living and half death which makes conventional divine help impossible to destroy them. Seeing an adult undead flea can lay approximately twenty to thirty eggs every few days, it makes for a hard time keeping up with their cycle to kill them all.
If left unattended or uncontrolled, the fleas will continue to drain the dwarven host of their life essence, and eventually kill them. Once this happens they burrow further into the dwarfs skin and dissipate, or dissolve releasing the dark magic used to keep them in a state of unlife and thereby passing this magic through the now dead dwarf which after a short period will awaken in a similar state of undead status thereby completing the cycle and the fleas purpose.