Possums are not established in Hawaii, and both the North American Opossum and Australian possums are prohibited species. Marsupials like the opossum are subject to strict regulations due to the state’s fragile ecology. The presence of any possum is considered a biosecurity threat, triggering immediate capture and eradication protocols.
Status of Possums in Hawaii
The North American Opossum, Didelphis virginiana, is the animal most commonly referenced when the term “possum” is used in the United States. It is classified as a non-native and prohibited species in Hawaii. State law prohibits the possession, sale, or transportation of this and other marsupials without specific permits for certified institutions, as codified under the Hawaii Administrative Rules, Title 4.
No breeding populations of possums are established in the wild across the Hawaiian Islands. Any individual found is considered a stowaway that arrived via cargo shipments, typically from the mainland United States. The Hawaii Department of Agriculture (HDOA) immediately responds to sightings to prevent establishment. Between 2005 and 2016, six opossums were captured, but recent years have shown an uptick, suggesting a persistent threat from incoming cargo.
Hawaii’s Unique Biogeography
Hawaii’s biological vulnerability stems from its extreme isolation, which led to a unique evolutionary history. Millions of years of evolution without land mammals or generalist predators created an ecosystem lacking natural defenses against invaders. Many native birds, for example, evolved to nest on the ground or in low-lying shrubs, unprotected from egg-eating mammals.
Introducing a generalist omnivore like the possum, which consumes insects, bird eggs, and fruits, would be ecologically devastating. The opossum’s opportunistic diet directly threatens Hawaii’s rare endemic flora and fauna, including ground-nesting seabirds and vulnerable native insects. The state is already considered the endangered species capital of the world, and a new predator could accelerate extinction rates.
The absence of native marsupials means there are no natural competitors or diseases to keep a newly established population in check. An invasive species finding a new food source without natural population controls can multiply rapidly, causing widespread disruption. This biological fragility is the reason for the state’s aggressive stance against introducing prohibited non-native animals.
How Hawaii Maintains its Isolation
Hawaii actively maintains its isolation through rigorous regulatory and enforcement mechanisms targeting invasive species. The state’s stringent quarantine protocols and inspection requirements are some of the strictest in the nation for all incoming cargo, baggage, and pets. The primary authority for this defense is the Hawaii Department of Agriculture, specifically the Plant Quarantine Branch.
Inspectors utilize various methods, including traps and visual inspections, focusing on areas like Honolulu Harbor, where the majority of international and mainland cargo arrives. When a possum is found, it is swiftly captured and often humanely euthanized. This is done to test for diseases like rabies, which the state is currently free of.
Laws governing the import of restricted animals are clearly defined, and high fines and penalties are associated with illegal importation. Anyone who spots an illegal animal is urged to call the state’s toll-free PEST HOTLINE, demonstrating the public’s active role in biosecurity. This combination of strict law, active inspection, and public vigilance forms a multi-layered defense against invasive animals.