Giant Gambian pouch rats -- among the largest muroid rodents in the world -- have hit Florida's Grassy Keys and are breeding despite efforts to eradicate them.

The African rodents, which weigh up to nine pounds, are a giant threat to crops and other animal species, including Burmese pythons, boa constrictors, Nile monitor lizards, vervet monkeys, the Daily Mail Reported.

There are growing concerns that the rats could reach Florida's mainland and spread vermin.

We thought we had them whipped as of 2009. ... In the early part of 2011, a resident emailed me and said he saw one of the rats. We were skeptical but went back and talked to people and [saw] there were rats that we missed, Scott Hardin, the exotic species coordinator for Florida's Fish and Wildlife Conservation Commission, told the Keys Nest.

Once the female rats were spotted again in 2011, conservation groups set out to kill them with poison-laced cantaloupe and peanut butter, but the pests outwitted their efforts and escaped before they started reproducing.

I would not imagine there's more than another couple of dozen at most. We've caught them all within a half-mile of each other. ... We think they have not moved far, but they clearly reproduced, Hardin told Keys Nest.

Gambian rats are not only a threat to the local ecosystem, but can even pose a threat to children. Last year, the rats killed two infants in southern Africa, according to the Huffington Post.

Here's five things to know about the rats:

Habitat: The Gambian rat originates from Africa and is usually found in a colony of up to 20, roaming thick forests and termite mounds.

Prey: The rodents are omnivorous, feeding on vegetables, insects, snails and crabs.

Threat: The rats used to be imported as pets, but were banned in the U.S. after they were found to be spreading monkey pox.

Reproduction: They can bear five litters in nine months with an average of four young per litter.

Appearance:  The rats have large ears and a tail covered by fine hairs. The feet are almost white and most of the tail is dark grey with the final third off-white.