A Rust Mite is smaller than a flea: a round, rust-red body like a fleck of old paint, with eight short legs that look as if they were already crumbling. Alone it is almost invisible. In numbers they show as a creeping orange bloom on a blade, a hinge, or the back of a hand, a stain that moves when looked at closely. A colony makes a faint dry crunching, like a dead leaf crushed very slowly, and smells of wet iron and old blood.

They would live at the edges of a Rustfall and be carried beyond it on the goods, beasts, and people that came out. Away from the incursion they would dry and crumble within days.

They go for strength. A mite on a farm cart crawls to the iron tyre, not the rotten board; on a man, to the sword hand and the knee. Where they settle they do not eat; they wear, and leave a spreading patch of corrosion behind them. They ignore what is already failing.

What they settle on gives way faster than it should: a well-forged blade pits and flakes in a night, a stout beam goes soft and crumbly, a hinge rusts through. On skin they leave dry, cracked patches like old leather, and the bone beneath grows brittle. Oil, wax, and sealing stop them where they meet it; they cannot get a grip on a well-oiled blade or a waxed hull, and a hand rubbed with tallow sheds them.

They give nothing. Smiths, soldiers, and carters would fear them most, since the best tools and the strongest arms go first. Refugees coming out of a Rustfall would bring them on their gear, and a town that took them in might find its gate-hinges and its smith’s stock flaking within the week. Against them, everything that came in would have to be oiled, and what could not be oiled burnt.

Smiths who met them would blame them for any blade that failed. Whether the mites are the spores of the Rust Flower hatching is not known, and see Knowledge of the Cosmos. The Rust-Hosts would crawl with them.