Rust Devil Rats

The first sign is the smell: an acrid, cloying sharpness that settles in the back of the throat like inhaling powdered iron. The second sign is the dust, reddish-brown trails along workbenches and storage shelves. The third sign is the blade that was reliable this morning now pitting at the edge. By the time anyone sees the rats, the damage is already done.
  Rust Devil Rats are oversized urban vermin that accumulate rust dust in their matted fur until every movement trails a cloud of corrosive particulate. Where Rust Devils nest, metal degrades. Tools pit. Weapons lose their edge. A Rust Devil's bite delivers rust-laden contamination directly into metal equipment, stripping reliability from weapons.
  Individually, a Rust Devil Rat is physically fragile. The threat is not the rat itself but what the rat does to your equipment over time. An infestation in a workshop or shipyard can render an entire inventory unreliable within days. The rats breed fast enough to make permanent eradication something closer to a dream than a plan.