While Hawai‘i Island (commonly known as the Big Island) is considered one of the safest tropical destinations in the world in terms of wildlife hazards, it is still home to several animal species that can pose risks to unwary visitors.
From venomous marine creatures to aggressive insects and invasive land animals, understanding the threats is key to staying safe while enjoying the island’s natural beauty. This guide provides an in-depth look at some of the most important species to be aware of on the largest island of the United States, especially for those hiking, snorkeling, or venturing off the beaten path.
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Tiger Shark (Galeocerdo cuvier)
The tiger shark is the most dangerous shark species in Hawaiian waters and accounts for the majority of shark-related incidents in the state. These large, solitary predators can grow over 6 meters or 20 feet in length and are known for their indiscriminate feeding habits, which include fish, turtles, seabirds, and occasionally inedible objects.
Although attacks on humans are rare, they do occur, especially in nearshore waters where sharks may be hunting or navigating murky conditions. Hawai‘i Island has recorded fewer shark attacks compared to other islands, but vigilance is still essential in areas like Kona, Hilo Bay, and near river mouths. Tourists are advised to avoid swimming alone, especially at dawn or dusk, and to avoid entering the water if they have open wounds or if local advisories are issued.
Portuguese Man o’ War (Physalia physalis)
The Portuguese Man o’ War, often mistaken for a jellyfish, is actually a siphonophore: a colonial organism made up of specialized individual animals called zooids. It floats on the ocean surface with a translucent, gas-filled bladder and long tentacles that can extend up to 30 meters or 100 feet. These tentacles deliver a painful sting using venom-filled nematocysts that can cause intense burning, welts, nausea, and in some cases, severe allergic reactions.
Stings can occur in the water or on the beach, as the tentacles remain potent even after the organism has died. Swimmers should check with lifeguards or local weather services for warnings, and in the event of a sting, affected areas should be rinsed with saltwater and not fresh water, which can exacerbate the venom release.
Cone Snails (Conus spp.)
Cone snails are among the most venomous marine animals in the world and are found in the tide pools and reefs of Hawai‘i, including the Big Island. While their beautifully patterned shells make them popular with shell collectors, they conceal a harpoon-like tooth capable of injecting a neurotoxic venom known as conotoxin.
Species such as the textile cone (Conus textile) can deliver venom potent enough to cause paralysis or even death in humans. These snails do not attack, but may sting when handled or stepped on. Tourists should never pick up live shells from the beach or tide pools, and children should be taught to avoid touching unfamiliar marine life.
Long-Spined Sea Urchin (Diadema setosum)
Known locally as wana, this species of sea urchin is easily recognized by its long, sharp spines and radial symmetry. These urchins inhabit coral reefs and rocky shorelines and are often hidden in crevices or tide pools, making them difficult to spot.
Stepping on a Diadema setosum can result in multiple puncture wounds, with some spines breaking off under the skin and causing prolonged pain, inflammation, or infection. While the venom is mild, the mechanical damage and risk of secondary bacterial infection can be significant. Wearing sturdy water shoes and watching your step when exploring intertidal areas are effective precautions.
Hawaiian Centipede (Scolopendra subspinipes)
The Hawaiian centipede is the largest and most aggressive centipede species found in Hawai‘i and can grow up to 20 centimeters or 8 inches in length. It is a fast-moving, nocturnal predator that preys on insects and small animals, but will bite humans if threatened or accidentally disturbed. The bite delivers venom through modified front legs (forcipules) and causes intense, burning pain, swelling, and occasionally nausea, dizziness, or fever.
Though not generally life-threatening, bites are extremely painful and can last several hours to days, sometimes requiring medical attention for allergic reactions or infections. Tourists should take care when hiking, especially in humid forested areas, and inspect bedding, towels, and shoes in rural accommodations.
Little Fire Ant (Wasmannia auropunctata)
An invasive species originally from Central and South America, the little fire ant has become a serious pest on the Big Island. These ants are just 1.5 millimeters in length but deliver painful stings that can result in itchy, raised welts that last for days. Stings most often occur when ants fall from trees onto people’s skin, such as when sitting under vegetation or camping.
Unlike larger fire ant species, Wasmannia auropunctata can infest homes, nurseries, and agricultural areas, posing both a health and ecological threat. Visitors should avoid sitting on bare ground in infested zones and report sightings to local environmental authorities, as eradication efforts are ongoing.
Feral Pig (Sus scrofa)
Feral pigs on Hawai‘i Island are descendants of domesticated pigs brought by Polynesians and European settlers. They are most commonly found in forest reserves, agricultural zones, and remote hiking trails. Though they generally avoid human contact, feral pigs can become aggressive if cornered or protecting piglets.
They have sharp tusks and powerful bodies and have been known to charge when startled. Hikers should make noise while walking to avoid surprising pigs and avoid approaching or feeding any wild animals encountered.
Culex and Aedes Mosquitoes (Culex quinquefasciatus, Aedes aegypti, Aedes albopictus)
Mosquitoes are present year-round on the Big Island and can transmit several diseases, including dengue fever and Zika virus, though outbreaks are infrequent. The Aedes aegypti mosquito is a known vector for dengue and is most active during the day, especially early morning and late afternoon. The Culex mosquito is more active at night and can transmit avian malaria, which, while not a threat to humans, affects native Hawaiian birds.
Tourists visiting low-lying, humid, or forested areas should wear insect repellent containing DEET or picaridin and wear long-sleeved clothing to minimize exposure. Standing water should be avoided, and accommodations should be screened or air-conditioned.
Lesser Brown Scorpion (Isometrus maculatus)
The lesser brown scorpion is the only scorpion species found in Hawai‘i, including on the Big Island. Originally native to Southeast Asia, it was unintentionally introduced and now resides primarily in dry, warm environments such as under rocks, bark, or debris. This species is relatively small, typically about 6 centimeters or 2 inches in length, and is light brown with a mottled pattern.
Though venomous, its sting is comparable to a bee sting for most people, causing localized pain, redness, and minor swelling. However, those with allergies or compromised immune systems may experience more significant symptoms, and children may be more sensitive. Scorpions are nocturnal and reclusive, so check shoes, clothing, and bedding if staying in rural or open-air places. Avoid handling rocks, logs, or garden debris with bare hands.
Box Jellyfish (Alatina alata)
Box jellyfish are among the most venomous marine animals in the world and are present in Hawaiian waters, though they are far more common around O‘ahu than the Big Island. Alatina alata, the species most frequently found in Hawai‘i, appears primarily in swarms approximately 8 to 10 days after the full moon. Their transparent, cube-shaped bodies are difficult to spot in the water, and their tentacles carry cnidocytes that deliver powerful stings, resulting in intense pain, welts, muscle spasms, and in rare cases, systemic reactions such as difficulty breathing or heart complications.
Most stings are not fatal, but they can be medically serious, especially for sensitive individuals. Sightings around Kona or Hilo are rare but not impossible, particularly during jellyfish influx periods. Check local beach advisories for jellyfish warnings, especially if swimming in the days following a full moon. Do not touch jellyfish, dead or alive, and seek medical assistance for any sting that causes systemic symptoms.
No Native or Wild Snake Species
Hawai‘i is unique because it has no native or established wild snake populations, making it one of the few snake-free regions in the world. This is due to strict environmental regulations and geographic isolation. The introduction of snakes could severely threaten native bird species and ecosystems, which is why it is illegal in the state.
While there have been occasional illegal imports or accidental introductions, such as the brown tree snake (Boiga irregularis), which has devastated native wildlife on Guam, there is no established snake population on the Big Island or elsewhere in Hawai‘i. The only snakes legally present are under strict control in zoos or scientific institutions. If you see a snake in the wild, report it immediately to the Hawai‘i Department of Agriculture, as it may be an illegal or invasive species.