Hawaii, known for its stunning landscapes, often leads visitors to wonder about predators. Its isolated geography and human history have shaped a unique predator landscape compared to continental landmasses. Both land and sea environments host various species considered predators, some native and others introduced.
Hawaii’s Terrestrial Ecosystem: A Unique Landscape
Hawaii’s volcanic origins and isolation profoundly shaped its native terrestrial ecosystem. For millions of years, species arrived sporadically, carried by wind, water, or on the wings of birds. This meant large land mammals and their associated predators, like bears or big cats, never naturally reached the islands.
The ecosystem became dominated by unique plant life, diverse insects, and a remarkable radiation of birds. Many native birds lost their ability to fly due to the absence of ground predators, making them vulnerable to later introductions. The Hawaiian hoary bat (Lasiurus cinereus semotus) is the sole native terrestrial mammal, an insectivorous species that hunts moths, beetles, and other insects using echolocation.
Introduced Land Species: The Uninvited Hunters
The arrival of humans profoundly altered Hawaii’s terrestrial ecosystems by introducing non-native species, some of which became significant predators. The small Indian mongoose (Herpestes javanicus) was brought in 1883 to control rat populations, but it primarily hunts during the day while rats are nocturnal. Instead, mongooses prey heavily on native ground-nesting birds, their eggs, and hatchlings, contributing to declines in species like the Hawaiian goose (nēnē).
Three rat species were introduced: the Polynesian rat (Rattus exulans), black rat (Rattus rattus), and Norway rat (Rattus norvegicus). These omnivorous rodents consume bird eggs, chicks, native snails, insects, fruits, and seeds, impacting native wildlife and plant regeneration. Feral cats (Felis catus), introduced by Europeans, are widespread across all main Hawaiian islands and are devastating predators of native birds and insects. They also spread the parasite Toxoplasma gondii, which can sicken and kill native birds, Hawaiian monk seals, and humans.
Feral dogs (Canis familiaris) also pose a threat to native wildlife. While the brown tree snake (Boiga irregularis) is largely contained to Guam, it remains a serious potential threat, with strict quarantine measures in place to prevent its establishment in Hawaii, as it could devastate bird populations. Coqui frogs (Eleutherodactylus coqui), introduced accidentally around 1988, are not large predators but consume vast quantities of native insects and spiders, impacting the food web and competing with native insectivorous birds. Their loud calls also create significant noise pollution.
Insects and arachnids also include introduced predatory species. While brown recluse spiders (Loxoceles reclusa) have been found, centipedes, specifically Scolopendra subspinipes mutilans, are common and can inflict painful bites. Invasive yellowjacket wasps (Vespula pensylvanica) have established large, persistent colonies, preying on native insects and spiders and even scavenging on vertebrates. These wasps disrupt native ecosystems by reducing native arthropod populations and competing for nectar resources.
Oceanic Life: Predators of the Deep
Hawaii’s surrounding ocean waters host a variety of predators. Approximately forty shark species inhabit Hawaiian waters, ranging from small deep-water pygmy sharks to large whale sharks. Commonly encountered nearshore species include whitetip reef sharks (Triaenodon obesus), sandbar sharks (Carcharhinus plumbeus), scalloped hammerhead sharks (Sphyrna lewini), and tiger sharks (Galeocerdo cuvier). These apex predators consume weak or sick animals.
Tiger sharks are considered the most frequently implicated in incidents with humans in Hawaii due to their size and varied diet, which includes fish, lobsters, birds, turtles, and carrion. Such incidents are rare, averaging about three to four per year, with fatal attacks being extremely uncommon. Barracudas (Sphyraena barracuda) are also present, known for their elongated bodies and sharp teeth, typically preying on smaller fish. Moray eels (Gymnothorax spp.) inhabit reef crevices and can deliver defensive bites if provoked, using their strong jaws to capture prey.
While not predatory in the conventional sense, certain marine organisms pose hazards to swimmers. Box jellyfish (Carybdea alata) and Portuguese man-of-war (Physalia physalis) have potent stinging cells. Box jellyfish stings can cause significant pain and linear marks, while Portuguese man-of-war stings, though rarely life-threatening, can be intensely painful and leave zig-zag marks. These organisms often wash ashore, particularly after certain lunar cycles or strong winds. Cone snails (Conus spp.) are another marine hazard; some species are venomous and can deliver a potent sting if handled, capable of causing serious medical issues.