In Hawai‘i the word “vermin” brings to mind two animals: the rat and mongoose. And let me tell you, these guys are much worse than any of those mainland attic dwellers and garbage eaters, like raccoons or skunks. Like them, rats and mongooses have also swarmed human-inhabited areas and have gotten into our trash. But unlike their mainland equivalents, they also have irreversibly damaged Hawaii’s unique biological diversity. And they’re not pau yet.

These two powerful invaders were a completely unexpected tag team. Originally, early Polynesian settlers introduced Polynesian rats to the Hawaiian Islands, followed by colonial Westerners that brought over two other species of rat. Although it is safe to assume that this invasive animal was an unintentional stowaway on voyaging ships, the mongoose was not. This weasel-shaped, beady-eyed carnivore was purposefully brought over by Hawaiian plantation owners, whose sugar cane crops were being destroyed by the rodents. The people expected the mongooses to control the skyrocketing rat population through predation.

Soon after however, the landowners discovered that mongooses were diurnal and only hunted during the day, while rats were nocturnal animals and only came out at night. As a result, the two animals barely crossed paths according to their daily schedules. By that time, it was too late to stop the momentum of the mongoose population growth. Oops.

And because the mongoose still needed a source of food, they instead turned to native Hawaiian birds and their nests.

Isolated native species are often completely helpless to any invaders because in a habitat initially without predators, there is no need to evolve survival mechanisms. As a result, these animals are unable to adapt quickly enough to maintain their numbers against introduced threats. Since its arrival, the exponentially expanding mongoose population has driven several native ground-nesting birds to either extinction or critically endangered status. Among these include the Nene goose and Newell’s shearwater, a Hawaiian seabird (which most of us haven’t even heard of, unsurprisingly). In 1999, it was estimated that the mongoose caused around $50 million in damages to Hawai‘i. We don’t even want to imagine what they’re costing us now.

Mongooses also now prey on the eggs of the endangered honu (sea turtle) as well. And to make matters worse, because the amount of sugar cane plantations on the islands has diminished in recent years, the rats are also turning to vulnerable native birds as a main food source. The birds have no rest, with both night and day predators to fend off. They are combatting the ultimate tag team of avian mass murder.

Invasive animals like the rat and mongoose cause a disturbance in Hawai‘i’s ecosystem, which is made unique by its diversity of species found nowhere else on the planet. They have a truly unparalleled negative impact on Hawai‘i’s natural environment. Efforts have been made to keep the mongoose population from infecting the two Hawaiian Islands still unexposed to its wrath. But there is potential that these attempts will soon be in vain.


“An Invader Advances in Hawaii.” The New York Times. The NY Times Co, 11 June 2012. Web. 25 May 2017.

“Mongoose.” Hawaii Invasive Species Council., 2017. Web. 25 May 2017.

“Mongooses in Hawaii Newspapers.” Hawai‘i Digital Newspaper Project. 2014. Web. 25 May 2017.