What Is the Most Resilient Animal? 10 Toughest Survivors

The tardigrade, or water bear, is the most resilient animal known. Dried out into a dormant state called a tun, tardigrades have survived temperatures close to absolute zero in the lab, pressures around six times those at the bottom of the deepest ocean trench, radiation doses hundreds of times higher than what would kill a person, and ten days exposed to open space in low Earth orbit.

The AnimalDex tier list answers a slightly different question: which animals in its catalog are toughest across a whole life in the wild, through cold, drought, hunger and injury. On that list the Crocodile ranks first, followed by the Polar Bear and Wolverine. The tardigrade is a microscopic invertebrate that sits outside that ranked catalog, so this article covers both answers.

Resilience means surviving hardship and coming back from it. It is not strength, which is about how much force an animal can produce. A tardigrade has almost no strength at all and survives conditions that would destroy an elephant.

Most resilient animals tier list (top 100)Strongest animal in the worldWhat is the most adaptable animal?Water bear (tardigrade) species page

Tardigrades are eight-legged micro-animals, usually 0.3 to 0.5 mm long, with more than 1,000 described species. They live in moss, lichen, leaf litter, soil, fresh water and ocean sediment, and they need a film of water to be active.

Their trick is anhydrobiosis, life without water. As their surroundings dry out, they pull in their legs, curl into a barrel-shaped tun and lose almost all of their body water. Metabolism falls to levels that are hard to detect. Tardigrade-specific proteins help hold cell contents together as they dry, and in the species Ramazzottius varieornatus a protein called Dsup binds to DNA and protects it: in a 2016 Nature Communications study, human cells engineered to make Dsup suffered about 40 percent less X-ray damage. Add water and a tun can be walking again within minutes to hours.

In 2007 the European FOTON-M3 mission carried dried tardigrades into low Earth orbit and exposed them to space vacuum and cosmic radiation for ten days. Many survived and reproduced afterwards, though the unfiltered solar ultraviolet killed most of those exposed to it (Jönsson and colleagues, Current Biology, 2008).

There is an important limit. Tardigrades tolerate extremes; they do not thrive in them. A 2020 study in Scientific Reports found that a day at about 37 °C killed half of active Ramazzottius varieornatus. Their record-breaking survival happens only in the dormant tun state.

Tardigrades do not beat extreme conditions by being strong. They survive by switching life almost off and waiting.

This is the same top ten as the AnimalDex most resilient animals tier list, in the same order. The Crocodile, Polar Bear and Wolverine lead. The list rewards two kinds of resilience: tolerance, which is enduring cold, heat, drought or hunger (crocodile, polar bear, wolverine, red kangaroo), and recovery, which is regrowing or repairing what is lost (sea cucumber, axolotl, octopus).

Resilience can also be social. Elephants and wolves get through hard seasons because the group holds knowledge and shares food, not only because each body is tough.

See all 100 on the most resilient animals tier list

CrocodilePolar BearWolverineElephantRed KangarooSea CucumberAxolotlGreen Sea TurtleWolfOctopus

The leaders on the tier list each survive a different kind of pressure.

The axolotl can regrow a leg, yet it is critically endangered in the wild. Resilience in one animal does not make a species safe.

Crocodile: built to outlast

Crocodilians come from a lineage that survived the mass extinction 66 million years ago that ended the non-avian dinosaurs. Their slow, cold-blooded metabolism lets large adults go months without feeding, their bony armour absorbs bites from rivals, and they recover from serious wounds in muddy water that would infect most animals. The saltwater crocodile, the largest living reptile, moves between rivers, mangroves and the open sea, removing excess salt through glands on its tongue.

Polar bear and wolverine: cold-country endurance

Polar bears are insulated by dense fur and a fat layer that can be around 10 cm thick. In Hudson Bay they spend about four ice-free months onshore eating little or nothing, and pregnant females den and fast for up to eight months while giving birth and nursing. Wolverines weigh only about 10 to 18 kg but cover huge territories in deep snow, scavenge frozen carcasses, and cache food in snow to eat weeks later.

Elephant and red kangaroo: getting through drought

Elephants dig for water in dry riverbeds and travel to remembered water sources. In a severe drought in Tanzania's Tarangire National Park in 1993, families led by older matriarchs lost fewer calves, a result published in Biology Letters in 2008. Red kangaroos rest in shade through the heat of the day, lick their forearms to cool down, and get much of their water from plants. Females can pause the development of an embryo, so breeding slows in drought and restarts when rain returns.

Sea cucumber and axolotl: coming back from damage

Many sea cucumbers expel part of their internal organs when attacked, leaving a predator with a mouthful while they crawl away and regrow the lost organs over the following weeks. Axolotls regrow lost limbs, the tail, parts of the spinal cord and heart, and tissue in the eye and brain, usually without scarring.

Several animals outside the top ten hold specific survival records. Most are small, and most survive by slowing their bodies down rather than fighting the conditions.

• Bdelloid rotifers

  Microscopic animals revived from Siberian permafrost about 24,000 years old, which then fed and reproduced (Shmakova and colleagues, Current Biology, 2021).

• Wood frog

  Freezes solid in winter. Its heart and breathing stop, ice forms in its body cavity, and glucose protects its cells until it thaws in spring.

• Arctic ground squirrel

  Lets its body temperature fall below 0 °C during hibernation, the lowest recorded for a mammal, and rewarms every few weeks.

• Naked mole-rat

  Survived 18 minutes with no oxygen in lab tests (Park and colleagues, Science, 2017), very rarely develops cancer, and lives more than 30 years.

• Cockroaches

  Tolerate radiation several times better than humans and can survive weeks without food, but they are far less tolerant than tardigrades.

Wood FrogNaked Mole-ratCockroach

The two words get mixed up because both describe something an animal can endure. They measure different things, and the best animals for each barely overlap.

Strongest animals tier listHow crocodiles dominate the water's edge

In the lab, tolerance is measured as the dose or temperature at which half of the test animals die, and how long they survive at a given level. In the field, resilience shows up in survival through droughts and hard winters, in how long animals live, and in how quickly they recover from injury or a population crash. Regeneration is measured by what grows back and how closely the new tissue matches the old.

The tier list blends these with what is known about each animal's survival in the wild, which is why large, long-lived species with a record of getting through hard conditions rank above animals with one extreme trick.

• Myth: cockroaches would survive a nuclear war

  They tolerate more radiation than people, but not the blast or heat, and many insects, such as some fruit flies and parasitic wasps, tolerate more radiation than cockroaches do.

• Myth: tardigrades are indestructible

  Active tardigrades die from heat that people survive easily. Their records are set in the dormant tun state, and even then exposure time matters.

• Myth: tardigrades live in space

  They survived ten days of exposure in a dried, dormant state. Nothing lives and reproduces in open space.

• Myth: the strongest animal is the toughest

  Large, powerful animals often need the most food and water, which makes them vulnerable in a drought. Small animals that can shut down often outlast them.