Stocky, aggressive shark up to 3.5 m. Uniquely tolerant of fresh water — found in Mississippi, Amazon, even Lake Nicaragua.

Top contender for most dangerous shark to humans. Hunts in shallow, murky water — exactly where people swim. Many attacks attributed to 'great whites' are actually bull sharks.

Shallow coastal waters, estuaries, rivers — Florida, Gulf of Mexico, Caribbean (Cuba, Bahamas, DR), Lake Nicaragua, Mississippi River, Pacific coasts of Mexico and Central America.

Aggressive and territorial. Tolerates salinity from 0 to 53 ppt. Attacks unprovoked more than other sharks.

Up to 5 m with vertical tiger-like stripes (fade with age). Eats almost anything — license plates, tires, and human remains have been found in their stomachs.

Second only to great white in unprovoked human attacks. Common in Caribbean and Hawaiian waters. Slow but powerful — strikes once and waits.

Tropical and subtropical waters — Florida, Caribbean, Gulf of Mexico, Hawaii.

Solitary, mostly nocturnal. Migrates long distances. Females birth up to 80 live pups.

Up to 3 m. The most commonly encountered large shark on Caribbean reefs. Often seen by divers in the Bahamas.

Generally non-aggressive, but documented attacks during shark feeding tours and on spear-fishers. About 30 unprovoked attacks recorded.

Coral reefs and continental shelves of the Caribbean — Bahamas, Cuba, Jamaica, DR, Belize, all major reef systems.

Diurnal. Apex predator on coral reefs. Often investigates divers but rarely aggressive without provocation.

Not a jellyfish but a colony. Distinctive blue-purple gas float with 30-metre tentacles trailing below. Drifts onto US Atlantic and Gulf coasts.

Excruciatingly painful sting causing whip-like welts. Rarely lethal, but several deaths recorded from heart failure or drowning after shock.

Atlantic and Gulf coasts — Florida, Texas, Louisiana, North Carolina; sometimes washes up by the thousands.

Drifts on wind via sail-like float. Cannot swim — entirely passive. Tentacles sting for weeks even after death.

Pale yellow-tan, 7–8 cm. The most venomous scorpion in North America. Glows brilliantly under UV light.

Neurotoxic sting causes severe pain, numbness, and in children — convulsions and respiratory failure. Antivenom dramatically reduces mortality.

Rocky deserts and palm oases of Arizona, southern Utah, southeastern California, parts of New Mexico and northern Mexico (Sonora).

Climbs walls, hides under bark and stones. Active at night. Sometimes enters homes. Can survive being frozen overnight.

Striking red-and-white striped fish with long venomous spines. Originally from Indo-Pacific; invaded the Caribbean and US Atlantic in the 1980s and is now devastating reef ecosystems.

Sting causes severe pain, swelling, sometimes anaphylaxis. Rarely fatal but ER visits common — and lionfish have no predators in their invasive range.

Invasive across Caribbean, Gulf of Mexico, US Atlantic coast from Florida to North Carolina.

Stationary among rocks and reef. Stings only when handled or stepped on. Females release 30,000 eggs every 4 days.

Disc up to 1.5 m with whip-like tail bearing a serrated venomous spine. Common in Gulf of Mexico and Caribbean — popular with tourists at 'Stingray City'.

Stings only defensively when stepped on. Spine drives deep, often breaks off. Steve Irwin's death is a textbook example of chest impalement.

Sandy and muddy bottoms of Gulf of Mexico, Caribbean, southeastern US Atlantic coast.

Buries in sand. The 'stingray shuffle' (sliding feet) prevents most stings. Eats clams, shrimp.

Reddish-brown ant 2–6 mm. Invasive from South America since 1930s; now infests southern US from Texas to Virginia. Aggressive when nest disturbed.

Stings cause burning pustules. Allergic reactions can cause anaphylactic shock — about 80 deaths per year in US attributed to fire ants.

Open sunny areas — lawns, fields, roadsides — across southern US, Caribbean, parts of Mexico.

Builds large mound nests up to 60 cm tall. Step on a mound, hundreds swarm out and sting in unison.