feldgeister
Humanity has a long history with harvest fields. Planting and harvesting grains was the first group act that let ancient humanity put down roots and settle in one place instead of following the seasons and the herds. For the first time, humanity was able to, en mass, set aside food against the starvation of the winter months. Planting and harvesting quite literally changed the face of the world and the fate of the people that lived on it. House clusters that didn't have to be temporary sprang up, towns and then cities followed. Society changed in a way that has to be mind boggling to try to fathom millennia later for most of us, so ingrained in this now standard 'normal' that we are. For the first time ever, humanity told the world how things were going to go instead of simply being at the whim of a changing environment. The old gods of the hunt and the wild places faded from their prominence as people gathered in settlements and imprinted order and routine on the world around them.
The old shadows of the wild places were fading - but that doesn't mean there were no new shadows taking their place in this new human order. Harvest, and the growing fields before it, suddenly held all the capricious danger that venturing out to hunt in the wild areas used to. Rain at the wrong time, drought, pestilence, enemies raiding or razing the fields full of food, blight or crop disease - the uncertainty of relying on hunting for survival was replaced with the uncertainty of fields surviving to harvest. And so, into those crop fields of grain and green, crept the spirits of the harvest, for good or ill, to remind humanity that everything came with a price and nothing was ever certain forever.
In the Germanic territories, these field spirits were called Feldgeister.
Sometimes they were also called Korndämonen. The corn demons.
And iron and other worked metals weren't going to save you either. Several of the Feldgeister used, or were even made of, iron.
As field spirits, the Feldgeister are broken down into what kind of field they live in. A Roggenwolf spirit for instance hunted the rye fields while a Getreidewolf hunted the grains. A Kornwolf stuck to the corn and Gerstenwolf stuck to the barley. Haferwolf for oats, Erbsenwolf for peas, Kartoffelwolf for potatoes, Graswolf for grass and even a Pflaumenwolf for plums. All of those were shaped like wolves and hunted children though the growing fields, ravenous and merciless.
Often, in fact, the field spirits took the forms of animals. There was a bear. There were cats. There were donkeys, pigs, goats and cows. If you name a common village animal, birds included, it probably had a Feldgeister taking its form while living in the fields outside of town. There was even a dog, that haunted the fields looking for little children to tickle to death.
Stealing and harming children was actually a common theme with the Feldgeister. There's nothing like warning children of things waiting to eat them to keep them from wandering into the fields unattended where careless feet could crush young plants or hungry mouths could snack down on a future harvest before it could be safely set aside for the winter months. There were quite a few hungry spirits waiting in the fields to snatch up children that wandered in hunting for the blue cornflowers that grew there.
It wasn't just children the Feldgeister were dangerous for. There was a female goat spirit that was fond of bringing evil with her. Hearing her cry in the spring was a full season of bad luck and if anyone dared imitate her cry to scare their neighbors, she would show up as a bloody coat draped over the offender's door if he was lucky and if he wasn't she would hunt him down, scratching him up on a good day, eating him alive on a bad one. She ran with the Wild Hunt on stormy nights and struck anyone foolish enough to look out their window into the darkness beyond. Anyone spotting her, day or night, was in for a bad time while their fields rotted and their cows refused to give milk. To hear her cry in autumn meant a long lean winter with rot in the hay. And yes, she too kidnapped, attacked or killed children she came across.
The Feldgeister didn't just take animal form however. They were fond of hybrid versions as well as straight up human forms too.
The Roggenmuhme, the 'rye aunt', took the form of an old woman with fiery fingers and sagging breasts that were often full of tar to the point of dripping as well as being tipped with iron. To run, she had to throw them over her shoulders. As humorous a mental picture as that may be, she used those long iron breasts to beat children to death and was capable of running as fast as a horse when she was chasing someone. She could blow a child's eyesight right out of their eyes and that was if she didn't crush them in an iron hug or grind them into mortar in her iron butter churn. She was the mother of the rye wolf and could become one herself. She also sometimes kept small, harmless seeming dogs she would use to lure little children into the field where they would become a meal for her. She was entirely black or entirely white in color and she carried a birch she used to strike lightning sparks.
Strangely, the Roggenmuhme wasn't entirely foreboding. Rotting fields meant she was punishing the farmer, but seeing a Roggenmuhme (presumably from a safe distance away) walking through your fields meant good luck and a strong harvest. She also played pranks on maidservants that weren't doing their work properly to keep them working hard.
Another human-looking spirit was the Hafermann, a sometimes anti-Semitic caricature, and corn demon that took the form of a man wearing a black hat and carrying a long iron tipped walking stick. He would kidnap or simply beat stray children that wandered into the field to death with his iron staff.
Sometimes the Feldgeister came in a more obscure form. Both the Bilwis and the Windsbraut took the form of whirlwinds, sweeping through the fields to cause destruction. Both could be defeated by throwing a knife with three crosses carved in it into them. This would either dissipate them, or they'd have to stop what they were doing and beg the farmer to pull out the knife since they were not able, being willing to exchange leaving him alone in trade.
Eventually, harvest time comes for everyone though, and the spirits of the Feldgeister fled into the interior of the fields as the reapers worked their way through the ripe stalks. The very last stalk of the harvest became their prison. Sometimes cutting it killed them. Sometimes it only put them to sleep, waiting through the winter until springtime, when the carefully saved last head of grain will be broken up into the newly plowed fields and the entire cycle will start all over again.