100+ Unique Facts About Animals

Animals have two main groups: vertebrates (with a spine) and invertebrates (without a spine). Mammals, birds, reptiles, fishes, and amphibians are the main types of vertebrate animals. Invertebrate animals generally include insects, arachnids (spiders, scorpions, mites, etc.), mollusks (snails, octopus, squid, etc.), and crustaceans (lobsters, crabs, shrimp, etc.).
Mammals and birds are warm-blooded animals that can adjust their body temperatures according to their surroundings. All the other animals are cold-blooded.
Most animals appeared during the Cambrian period around 540 million years ago, in duration of 20 to 25 million years. It is known as the Cambrian explosion and is the main event used by creationists to deny Darwin’s theory of evolution. (Source)
Pompeii worm is the earth’s most heat-tolerant animal that can live at a temperature of 176 F (80^o C). The bacteria on its body help the worm to withstand this extremely high temperature. (Source)
Northern pseudoscorpion, a tiny arachnid, can survive without breathing for 17 days. They can live underwater for 17 days in the absence of oxygen.
In 2010, scientists discovered the first animals that can live without oxygen. Three species of Loricifera inhabit the bottom of the Mediterranean Sea, a place without oxygen. They can live, reproduce, and molt in this harsh environment due to the presence of hydrogenosomes (that power a cell without oxygen) instead of mitochondria in their bodies. (Source)
The Blue whale is the largest animal ever to live on earth. It is far bigger than any other (extant or extinct) marine and land animal.
The Colossal Squid is the largest known invertebrate. It has a maximum length of around 45 feet and weighs up to 750 kg.

The jaws of ragworms are extremely strong but very light compared to such materials in other animals that contain calcium. It is due to a large quantity of a protein (histidine) that binds tightly with zinc. The combination of strong and light teeth makes it a demanding material for aircraft.
The dog was the first pet animal on earth. Humans domesticated dogs between 13,000 and 30,000 years ago. The domestication of sheep, goats (11,000 years ago), and cats (9,000 years ago) started later. (Source)
Around 200 species of animals and plants are becoming extinct every day. This extinction rate is 1,000 times faster than the natural rate. (Source)
Animal life is also present in the depth of the Mariana trench, the deepest known place on the earth’s surface. Some animals in this extreme depth include sea cucumbers, shrimps, and a few others. (Source)
Colossal Squids have the largest eyes among all animals. The diameter of the colossal squid’s eye is 11 inches (27 cm). (Source)
Scientists have discovered “good bacteria” in at least 25 deep-sea sponges. Experiments show that these bacteria can kill dangerous antibiotic-resistant bacteria like C.difficile and MRSA (methicillin-resistant Staphylococcus aureus). (Source)
Genetic studies prove corals are the longest-living animals on earth. Some of them can live for up to 5,000 years. (Source)
Almost all the longest-living animals on earth are aquatic. These include immortal jellyfish, sponges, ocean quahog clams, Greenland sharks, and bowhead whales. (Source)
It is a common belief that sponges are the first animal on earth. But recent studies show that the earliest animal could be comb jelly. (Source)

Comb jelly could be the first animal on earth
Australian Box Jellyfish is the most venomous marine animal. The venom in this marine animal can kill a human or animal within minutes. (Source)
There are more than 2,000 species of jellyfish. All these jellyfish produce venom, but only a few are dangerous to humans. (Source)
Jack jumper ants have the lowest possible number of chromosomes among multicellular animals. Their chromosome number is 2n = 2. (Source)
Olm, a blind cave salamander, can remain alive for 12 years or more without eating anything. (Source)
Several animals lack color vision and can only see in black and white. This Monochromatic vision is present in animals such as bats, raccoons, seals, sea lions, walruses, dolphins, whales, a few fish, etc. Humans and most other primates are trichromats that can see color vision. Cats, dogs, and a few other animals are dichromatic with limited color vision. (Source)
Just a few animals can see UV light. These include butterflies, reindeer, bees, a few species of birds, etc. (Source)
Few animals can see infrared light. These include snakes, fish, frogs, and blood-sucking insects. (Source)
Several mammals, birds, reptiles, and fish have a third eyelid. This thin membrane protects the eyes from debris, enables them to see underwater clearly, and sharpens their vision by providing moisture to the eyes. (Source)
Few fish species (tuna and pelagic sharks) and reptiles (Tuataras, lizards, frogs, etc.) have three eyes. This third eye (known as a parietal eye) is at the top of the head. This additional eye is not for vision but helps to adjust the circadian clock.

Opossums have the shortest gestation period among all animals. The female opossum will give birth to a child after 12 to 14 days of pregnancy.
The Giant armadillo has the longest claws-to-body ratio (22%) in the animal kingdom. These are the longest claws-to-body ratio for any animal in history. (Source)
Starfish, sea cucumbers, salamanders, and a few other marine and land animals have a strong ability to regenerate. They can regenerate their lost limbs and other body parts.
Salamanders have the extraordinary ability to regenerate their limbs and parts of their major organs (including the brain and spinal cord). They do so by using their immune system. (Source)
Asexual reproduction is possible in various animals. Females of several insects, fish, birds, and reptiles can reproduce without mating with male partners. (Source)
According to research, sexual reproduction started in the animal kingdom around 540 million years ago. The first animals to reproduce sexually were tube-like creatures known as Funisia dorothea. (Source)
Bottlenose Dolphins have the longest social memory among all animals (after humans). They can recognize the whistle of other dolphins even after 20 years of separation. (Source)
Jellyfish, sea stars, sea cucumbers, sea urchins, corals, and a few other simple animals are without brains. These animals can easily do all the necessary things to survive even in the absence of a brain. (Source)
Mantis shrimp have the most powerful punch in the animal kingdom. These marine animals can break the hard shells of crabs, clams, and other big animals through a punch equivalent to the trajectory of a 0.22 caliber bullet. They also contain up to 16 color-receptive cones in their eyes, the highest on earth. It assists them in viewing color vision, UV light, and polarized light. (Source)
Mantis shrimp have the strongest punch and the best vision
Pistol shrimp is the loudest animal relative to its size. Its claws can produce a sound of 3800dB per kg of its weight. Comparatively, the loudest animal on land relative to its size is the howler monkey, emitting a sound of 11dB per kg. (Source)
Hagfish is the only known animal having a skull without a vertebral column. (Source)
Atretochoana is the largest lungless tetrapod. Due to its resemblance to the human penis, it is commonly known as a “penis snake”. (Source)
In some animals, the gender of an embryo is affected by the temperature of the embryo’s environment. Temperature-dependent sex determination (TSD) has been observed in many species of reptiles (crocodiles, turtles, and a few lizards) and fish. (Source)
Sea turtles, salmons, and some other animals can use the earth’s magnetic field for navigation. (Source)
The bite of a Brazilian wandering spider, a dangerous venomous spider, gives hours-long painful erection to male victims. It works differently compared to Viagra and other such drugs. This venom might prove beneficial for erectile dysfunction in the future. (Source)
Parrots, bats, and a few other animals eat dirt. They do so either for nutrition or detoxification purposes. (Source)
Few animals (Glass frog, glass octopus, moon jellyfish, glasswing butterfly, ghost shrimp, etc.) have transparent bodies. Their internal organs (liver, heart, GI tract, etc.) are visible from the outside. (Source)
Chinese giant salamander is the world’s largest amphibian, with length and weight up to 5’9” and 65 pounds, respectively. This strange animal can produce several sounds, including crying, hissing, barking, and whining. Due to this characteristic, its Chinese nickname is “the infant fish.”

Bryostatin 1 is a chemical compound expected to be a potent anti-cancer drug. This compound was initially extracted in the 1960s from a bryozoan (moss animal).
Some animals can change their skin color through their diet. These include flamingos, canaries, yellow goldfinches, northern cardinals, shrimp, nudibranchs (mollusks), ghost ants, salmons, and humans. (Source)
Spider silk is five times stronger than steel. There are plans to use spider silk in future bulletproof jackets. (Source)
Few birds, mammals, insects, and fish suck the blood of other animals to fulfill their dietary needs. Vampire bats, sea lamprey, candiru fish, vampire moth, and vampire ground-finch are some examples of these blood-sucking animals. (Source)
Black piranhas have the strongest bite relative to body size among all living animals. The bite force of this freshwater fish is up to 40 times its body weight. This bite is more powerful than that of famous extinct animals (T. rex dinosaur and megalodon shark) and three times more powerful than the bite of an American alligator. The reason behind this powerful bite is its extraordinarily big jaw muscles. (Source)
Limpets, aquatic snails, have the strongest teeth in the animal kingdom. These snails use their teeth to get food (algae) from rock surfaces. These teeth are made from a material considered the strongest biological structure on earth. (Source)
According to a discovery, a jawless vertebrate had the sharpest teeth among animals ever existed. This eel-like creature lived earlier than 200 million years ago. (Source)
Bowhead whales have the largest mouth among all the animals. It uses this huge mouth to eat around 2 tons of food daily. (Source)
Limulus amebocyte lysate is a clotting agent used to test the presence of dangerous bacteria on antibiotics and kidney machines. This clotting agent is present in the blood of Atlantic horseshoe crabs.

Leeches suck blood, and this ability has been used to treat several blood-related diseases in humans since ancient times. The anticoagulant Hirudin is extracted naturally from the salivary glands of leeches.
Apart from mammals and birds, females are usually larger than males in most other animal species (most reptiles, amphibians, fish, insects, arthropods, worms, etc.). (Source)
Moths can hear the sound of 300 kilohertz (kHz). It is the highest known frequency of sound that any animal can hear. Bats (250 kHz) and dolphins (160 kHz) also have exceptional hearing limits. (Source)
Several animals (birds, reptiles, etc.) lack external ears. These animals use various body parts and methods to hear and distinguish between different sounds. (Source)
The Blood color of animals is not always red. Animals can have blood of various colors, including yellow (beetles, sea cucumber), green (marine worms, leeches), blue (spiders, octopuses), and purple (peanut worms, penis worms) due to different types of blood proteins in their bodies. (Source)
Nematodes, flatworms, and cnidarians (corals, jellyfish, and sea anemones) are the only animals that don’t have blood and circulatory system. They obtain oxygen and nutrients directly from the water where they live. (Source)
Crayfish and lobsters can swim forward and backward with their swimmerets and flips of the abdomen, respectively. Lobsters can also walk in any direction thanks to their ten walking legs. (Source)
Bivalve mollusks can play a vital role in identifying metal pollution in waters where they are present. They ingest these pollutants that remain in their systems. These metals do not cause serious ill effects in these animals. (Source)
Krill can eat and digest micro-plastic into nano-plastics. This ability can prove helpful in reducing plastic pollution in oceans. (Source)

Krill can reduce ocean plastic pollution
According to estimates, the population of Antarctic krill is around 500 trillion, the highest in the animal kingdom. (Source)
Nematode roundworms are the most abundant animals on the planet, as they constitute 80% of all the animals on earth. These animals account for 90% of all the life present in ocean sediment. They are present almost everywhere in marine water, freshwater, polar regions, mountains, deserts, etc. (Source)
Some animals eat their feces, soil, and toxins. Rabbits, hares, and several other small and medium-sized herbivorous animals eat their poo. Many birds and primates eat soil, while few insects consume a toxic diet.
Few animals have survived all types of dangers and are leading their taxonomic category in population. These include ants (insects), copepods (crustaceans), lightfishes (fish), frogs (amphibians), viviparous lizards (reptiles), red-billed quelea (birds), and brown rats (mammals). (Source)
Most animals use water for swimming, but several can also walk on water. More than 1,200 animal species can do so as gliders or slappers. This ability is present in both small (insects and spiders) and large animals (reptiles, birds, and mammals). (Source)
Few fish, mammals, and insects have Electroreception capacity. These animals use this feature to detect prey or other food sources. (Source)
Venoms and poisons from animals have several medicinal properties. At least 11 toxin-based drugs have been derived from snakes, lizards, leeches, and cone snails. Bee venom has anti-wrinkling effects. (Source)
Studies have proved that all types of octopuses and cuttlefish (along with a few squids) are venomous. (Source)
Corals are marine invertebrate animals that remain motionless underwater. They build structures known as coral reefs, made up of calcium carbonate, that act as a housing place for many fish species and protect coastlines by absorbing wave energy.

Paedophryne amanuensis is a species of frog living in Papua New Guinea. It is the world’s smallest vertebrate animal, with a length of just 7.7 mm (0.3 inches).
Kangaroos, wallabies, seahorses, horned marsupial frogs, and a few other animals have pocket-like structures on different parts of their bodies. These pouches are used to perform various functions.
Zombie (or bone-eating) worms are known for living in the bones of whales, fish, and other animals. These worms dissolve bones through the secretion of an acid that results in the death of the host animal. (Source)
Few mammals and birds employ the feature of echolocation (finding objects through echo) to find food in their environment. It is a necessity in caves, underwater, and other dark locations. (Source)
Several birds, insects, mammals, and reptiles eat medicinal plants for self-medication. They do so to treat diseases, remove the venom, aid digestion, kill parasites, and solve pregnancy issues. (Source)
Few birds (peregrine falcon, blackbird, wild duck), marine mammals (dolphins, beluga whales, sea lions), and reptiles (crocodiles) keep their one eye and half brain open while sleeping. (Source)
Coconut crabs, the largest crabs on earth, have the strongest pinch per body mass of any animal. This force is even stronger than the bite force of all animals except alligators. (Source)
In 2021, scientists discovered a 95-mm-long millipede with 1,306 legs, the highest in the animal kingdom. The previous record holder was also a millipede species with 750 legs. (Source)
Poison dart frogs are the most poisonous animals on earth. The poison on these brightly colored frogs is so dangerous that consuming even a small amount can cause death.
Mangrove tunicate (also known as sea squirt), a marine invertebrate animal, contains a compound named ET-743. This compound can kill cancer cells. (Source)
Tunicates are the only cellulose-producing animals
Tunicates (or Urochordates) are also the only animal that produces cellulose. (Source)
Few animals (horned lizards, crickets, etc.) eject venomous blood from their eyes as a defensive technique. It is known as reflex bleeding or autohemorrhaging, which affects the oral receptors of predators. (Source)
Rabbits and parrots are the only two animals that can see behind without turning their heads. It is possible due to the position of their eyes. (Source)
Most animals can see through their eyes, but some animals can see without eyes. These include animals without eyes and those having functional eyes. A few of these animals include sea urchins, hydras, scorpions, swallowtail butterflies, a few mollusks, etc. (Source)
The skin of octopuses is made from a light-sensitive pigment that is present in the eyes. Therefore, it is a possibility that these animals use their skin to see. (Source)
Platypus, echidnas, and around 25% of species of fish are the only vertebrate animals that don’t have a stomach. (Source)
Only a few animals have been found to recognize themselves in mirror tests. These include ants, Asian elephants, bottlenose dolphins, Eurasian magpies (a bird in the crow family), manta rays (a fish), and others. (Source)
Few animals are considered herbivores (plant-eaters) but eat flesh occasionally. Some of these include lorikeets (a parrot), deer, cows, sheep, etc. (Source)
Few tortoises, frogs, mice, and rats can live without drinking water for years. These animals can conserve a large amount of water in their bodies that can last for several years.
A kangaroo rat can live for up to 10 years. This rodent can live its entire life without drinking water. They can fulfill their water requirement through (water present in) the seeds and beans they eat.

Kangaroo rat can live without drinking water for years
Several animals change the color of their skin or hair in different seasons, especially those living in snowy areas. These animals turn their body (or hair) color to white in winter and dark in the summer season. (Source)
Coloration is widespread in the animal kingdom, but the procedure is different in warm-blooded and cold-blooded animals. Mammals and birds change their color by producing a new coat of fur and feathers. On the other hand, fish, reptiles, and amphibians change their body color through the bichrome in their skin cells. (Source)
Few species of fish, crabs, ants, and other animals grow their food by farming or livestock. (Source)
Kangaroos and emus are the two known animals that cannot walk backward. However, it is a wrong perception that penguins and alligators are incapable of moving backward. (Source)
Wars and battles are common in several animal species. Ants invade termites and other ant colonies, hornets assault honeybees, and chimpanzees raid neighboring colonies. (Source)
Studies show that apes and rats are the only known animals that can laugh. Experiments on these animals can assist in developing antidepressant medicines for humans. (Source)
Few animals (snakes, ducks, frogs, lizards, etc.) swallow their food whole. They do so either due to the absence of teeth or because their teeth cannot chew the food.
Fruit flies were the first animals launched into outer space in 1947. Many other animals also entered space later. These include mice, monkeys, dogs, cats, rabbits, tortoises, spiders, fish, jellyfish, etc. (Source)
Some invertebrate animals practice sexual cannibalism, where females eat their mates during or after mating. Animals with this behavior include black widow spiders, jumping spiders, golden orb spiders, praying mantis, the Chinese mantis, green anacondas, and scorpions. (Source)
Asian glass lizards have the longest tail by body length. Jerboa, spider monkeys, whiptail rays, and ribbon-tailed astrapia also have extraordinarily long tails. (Source)