|Images of rust monsters|
Source: Bestiary, pg(s). 238
The bizarre rust monster is much feared by adventurers.
A rust monster has a vaguely insect-like appearance. It is normally red-orange in colour, has four legs, twin feathery antennae, and a long tail ending in a twitching propeller-like tuft. It is covered in armoured plates. A typical specimen is five feet in length and weighs two hundred pounds.
The origins of the rust monster are unknown. Some speculate that may be descended from crustaceans, whilst others suggest they may be from the Elemental Plane of Earth. One theory is that they were deliberately introduced into Golarion for some unknown purpose.
A rust monster's body can store vast amounts of energy, which it broadcasts as an electromagnetic field – particularly through the antennae. Metal objects in contact with the field experience greatly accelerated oxidisation and release vast amounts of heat. The rust monster gains sustenance from this heat, and also eats the waste metal in order to obtain needed minerals.
Excess metal is used to form the creature's protective plates. Excess energy is shed by its unusual tail.
Rust monsters are continually hungry and always attempt to consume as much energy as possible by oxidising any metal it encounters.
Habit and society
Rust monsters are basically solitary, but large concentrations of metals may attract several at once. They generally live underground, preferring iron-rich mountain regions.
A rust monster who considers itself to be extremely well fed will search out the largest mate it can find. They are hermaphrodites, with both mates giving birth to litters of ten to twelve "nymphs". The pair stay together for about a year, until the young have reached adult size. It is unclear how long a rust monster can live for, but there are some indications that they can live for several centuries, perhaps longer.
Rust monsters can scent metal from up to ninety feet away. They can bite foes, but their jaws are weak.
The touch of their antennae can turn metal items into useless piles of rust in seconds. 
There are cat-sized aquatic rust monsters who scavenge the ocean floor.
Some rust monsters disperse excess energy by giving off bursts of electricity, which can be dangerous for those in close proximity.
However, the most dangerous type of rust monster is the rust lord. These creatures are bigger, tougher and more powerful than normal rust monsters, and supplement their diets by consuming the iron in the blood of living creatures – and their ability to sense metals is so developed that they can sense metallic blood to a range of one hundred feet.
Rust monsters are a major threat to dwarf societies. Some engage in ritualised rust monster hunts. Young dwarves strip naked, paint their bodies and arm themselves only with stone-headed spears and axes.
Some dwarven miners use rust monsters to lead them to ore deposits.
Rust monsters and dwarves clashed long before the Quest for Sky, and they are common in the vicinity of the Sky Citadels. Urgir, in the Hold of Belkzen, suffers regular tremors due to the countless rust monsters eating away at its metallic foundations.
Some believe that the decay caused by rust monsters is part of a long-term plot to free Rovagug from imprisonment. This has not gained mainstream acceptance, but the church of Sarenrae offers bounties for rust monster heads. Rust monsters are also particularly unpopular with followers of Gorum, Torag and Droskar.
- James L. Sutter. (2009). Rust monster. Dungeon Denizens Revisited, p. 53. Paizo Publishing, LLC. ISBN 978-1-60125-172-5
- James L. Sutter. (2009). Rust monster. Dungeon Denizens Revisited, p. 54. Paizo Publishing, LLC. ISBN 978-1-60125-172-5
- Jason Bulmahn. (2009). Pathfinder RPG Bestiary (First Edition), p. 238. Paizo Publishing, LLC. ISBN 978-1-60125-183-1
- Joshua J. Frost. (2009). Bulette. Dungeon Denizens Revisited, p. 55-56. Paizo Publishing, LLC. ISBN 978-1-60125-172-5
- James L. Sutter. (2009). Rust monster. Dungeon Denizens Revisited, p. 56. Paizo Publishing, LLC. ISBN 978-1-60125-172-5