What these animals lack in size, they make up for in their ability to make you wish you were dead, thanks to their painful bites and stings. Sometimes, these tiny creatures can even kill.
1. Irukandji Box Jellyfish // Carukia barnesi and Other Species
Believed to be one of the most venomous organisms in the world, Irukandji jellyfish—encompassing about 16 species of box jellyfish—are smaller than a peanut. They thrive in warm waters around Australia’s Great Barrier Reef. The hard-to-see creatures are outfitted with four hair-like tentacles that trail behind its body and have the ability to fire their stingers into their victims. If you're hit, you will experience what is described as “the worst pain of your life—pain so intense that the maximum dose of morphine barely takes the edge off.” According to the documentary Killer Jellyfish, whether you live or die from an Irukandji sting depends on your current state of health as well as “your blood vessels' ability to handle the pressure.” There is no antidote for an Irukandji sting. Beyond managing symptoms with strong painkillers, you simply must wait it out.
The Pain: The jellyfish's sting causes a unique set of ultra-painful symptoms dubbed "Irukandji syndrome." At first, the sting doesn't hurt much. You may experience some swelling along the site of contact and some minor discomfort. Five to 120 minutes later, though, the real pain sets in. Victims will start to experience a severe backache, headache, or shooting pains in their muscles, chest, and abdomen. Additional symptoms may include nausea, restlessness, and vomiting. If left untreated, the venom can lead to pulmonary edema (a build-up of fluid in the lungs), cardiac arrest, and death.
But Wait There's More: Certain species of box jellyfish can swim almost as fast as an Olympic swimmer, giving them the ability to navigate through the water at speeds of up to 4.5 knots (about 5.2 mph).
2. Asian Giant Hornet // Vespa mandarinia
The Asian giant hornet—a.k.a. murder hornet—is 2 inches long with a wingspan of around 3 inches and an oversized mandible with a strong black tooth. These giants of their genus have the ability to dispel venom with an enzyme so strong that it’s said to be able to dissolve human tissue. The Asian giant hornet kills more people each year than any other animal in Japan, where it's most common. The hornet’s preferred victims are honeybees. Each hornet has the ability to take out around 40 European honeybees in a mere 60 seconds. While they don’t tend to go after humans, an Asian giant hornet will sting you if you aggravate it, and running away from them won't help: these creatures can fly at speeds of 25 mph.
The Pain: “It was like having red-hot thumbtacks being driven into my flesh,” Conrad Bérubé, a beekeeper in Nanaimo, British Columbia, told The New York Times.
But Wait There's More: The murder hornet's range is expanding. In 2019, entomologists at Washington State University announced two sightings of the hornet near Blaine, Washington. Nests of the insects, which probably arrived in shipments of goods from Asia, were also found in British Columbia. Officials have urged citizens scientists to report any sightings. In Asia, in addition to Japan, the Asian giant hornet has also been spotted in Russia, Korea, China, Taiwan, Nepal, India, and Sri Lanka.
3. Candirú // Vandellia cirrhosa
Candirú are toothpick-sized catfish native to slow-moving waterways in the upper Amazon and Orinoco river basins of South America. These inch-long parasites feed mainly on blood, can often be found inside the gills of other fish, and have been known to swim up human urethras. In 1877, a Dr. Castro performed one of the first known extractions of a candirú, "which had penetrated [the woman's urethra] during [urination] while bathing in the river. The patient experienced cruel suffering for, since I had to drag the animal out, the extraction was difficult and the mucus membrane was lacerated.”
The Pain : Once the candirú travels up one's urethra, it spreads its spiked gills and lodges itself in the duct. Its presence can lead to inflammation, hemorrhage, severe pain, and, in the worst-case scenarios, amputation or death.
But Wait There's More: The fish is rumored to be attracted to the smell of urine. Allegedly, it will even jump out of the river and into the urethra of a man peeing at the water’s edge. In reality, candirú track down their blood meals by sight and chemical cues and are incapable of physically swimming up a stream of urine.
4. Bullet Ant // Paraponera clavata
The bullet ant, found in the tropical rainforests of Central and South America, boasts the most painful insect bite in the world. Their venom contains a neurotoxic peptide that kills the caterpillars and other small critters the bullet ant normally preys upon. But for humans, one sting will cause swelling and eye-watering pain for an entire day. Aggravating one of these creatures—which are also Earth's biggest ants—is something you’ll regret for a while.
The Pain: If these ants feel threatened, they use their mouths to grab onto you before delivering the venomous stings. Entomologist Justin Schmidt, originator of the Schmidt Pain Scale for Stinging Insects, describes it as "pure, intense, brilliant pain. Like walking over a flaming charcoal with a 3-inch nail embedded in your heel."
But Wait There's More: The Sateré-Mawé people in Brazil's Amazon rainforest give bullet ants a special role in their traditional coming-of-age ritual. A boy around 12 years old must stick his hands into a pair of woven gloves filled with bullet ants. The boy must do this 20 times for 10 minutes at a time. This excruciating trial is meant to demonstrate that life without suffering is not worth living.
5. Golden Poison Dart Frog // Phyllobates terribilis
Phyllobates terribilis is the most poisonous amphibian on the planet. The tiny frog is designated endangered or critically endangered due to its limited range in a coastal region in southwest Colombia. One golden poison dart frog, which grow to a maximum of 2 inches long, may contain enough poison to kill 20,000 mice. The Indigenous Emberà tribes in Colombia have traditionally used the poison on the end of their blowgun darts.
The Pain: The golden poison dart frog's skin is saturated with an alkaloid poison containing batrachotoxin, which prevents nerves from transmitting impulses. People or animals who come in contact with the frog may experience muscle contraction and convulsions, and even die. The poison is about 20 times more toxic than a typical poison dart frog.
But Wait There's More: The golden poison dart frog likely gets its toxicity from its prey, specifically mites. The frog then secretes the mites' toxic compounds through its skin. Golden poison dart frogs held in captivity, which eat a mite-free diet, will not be nearly as toxic.
A version of this story ran in 2013, it has been updated for 2022.