A rural insect breeder is under scrutiny after wildlife officials discovered a sprawling collection of exotic cockroaches worth thousands on the black market.

Wildlife officers have busted an illegal cockroach-breeding operation in rural Australia, seizing a skin-crawling haul worth more than $100 000 on the black market for exotic bugs.

More than 100 000 contraband cockroaches were found in a raid on a commercial breeder in the town of Bathurst, west of Sydney, Australia's environment department said on Friday.

They found Madagascar "hissing" cockroaches, a bulky insect named for its noisy defence mechanism, and dubia cockroaches, an invasive critter bred as a snack for pet lizards.

Photos showed one of the seized Madagascar cockroaches was almost big enough to completely cover the palm of an adult hand.