Stock Animal Facts

"''I know two things about the horse

And one of them is rather coarse.''"

- Naomi Royde-Smith

Whenever certain animals are mentioned, works (especially educational ones) will feel the urge to say a certain fact about them. Oftentimes it's intended to sound like something surprising or fascinating, which in general it would be if you didn't hear it every time that animal was mentioned in every work. With many Seldom Seen Species, their stock facts may be the only thing anyone (barring specialists) can ever say about them. See Somewhere This Index Is Crying if the stock "fact" about an animal is false. Can overlap with You Fail Biology Forever if it is clearly false. Occasionally a victim of Science Marches On.

Can overlap with Stock Animal Diet and Stock Animal Behavior.

Note: As this trope is based on its ubiquity, the only works that should be listed are aversions, subversions, lampshaded examples, in-universe examples, and other variants.

Mollusks

 * The giant squid has eyes the size of dinner plates. No one has seen one alive. (Until 2004.)
 * Snails leave behind a trail of slime that hardens and turns silver.

Annelids

 * Earthworms can regenerate (many other invertebrates can, but earthworms are perhaps most well known for it).
 * However, the common idea that cutting an earthworm in half will result in two earthworms is basically false; it's next to impossible for the half without a brain to grow a new one.

Insects

 * Insects have six legs and are divided into three body segments.
 * There are more insects (and arthropods in general) than any other type of animal on Earth.
 * Caterpillars become butterflies through metamorphosis. (Most other insects also go through metamorphosis, but it's always butterflies.)
 * Honeybees die after stinging. Somewhere an Entomologist Is Crying if the same is said about bumblebees or wasps. Also, the death is because it can't extract itself from a sufficiently thick-skinned animal; they can still sting other bees without a problem.
 * Mosquitoes are the most dangerous animals on Earth by number of deaths caused.
 * Some prehistoric dragonflies were the size of hawks.
 * Cockroaches have been around "longer than dinosaurs". If you cut a cockroach's head off it can still survive for a few days.
 * Ants are really strong and are some of strongest animals for their size.
 * The rhinoceros beetle is the strongest animal of its size.
 * Fleas can jump really really high for their size.
 * If this kind of insect was the size of a human, it'd be able to jump this high/lift this much/run this fast.
 * The reason it can't happen is pretty much a stock fact too by now.
 * Only female mosquitos bite.
 * Female praying mantids actually bite off the male's head after mating.
 * Contrary to popular belief, a wild beehive does not resemble a hornet nest.

Arachnids

 * Spiders are not insects, they're arachnids because they have EIGHT LEGS (well, there's more to it than that, but very simplistic differences are often pointed out).
 * Tarantulas are not actually all that dangerous.
 * Scorpions glow in the dark under a blacklight.
 * Black widow spiders are so-called because the more venomous female kills the male after mating.

Echinoderms

 * Sea stars feed by expelling their stomachs onto their food. This is actually only true for some sea star species.
 * Sea cucumbers expel their own guts as a distraction if attacked.
 * If a sea star is cut in half, then the two halves will become individual sea stars.

Fish

 * Fish are vertebrates with gills.

Cartilaginous fish

 * You're more likely to be killed by lightning/bees/cars than to be killed by a shark.
 * Sharks have been around "longer than dinosaurs". Technically true, but they haven't "remained unchanged" as many would have you think.
 * The whale shark is the largest living fish, but eats only plankton.
 * The basking shark is the second largest.
 * No one knows what the oddly shaped head of hammerhead sharks is used for (which is actually not true).
 * Tiger sharks can eat ANYTHING.
 * Sharks frequently lose their teeth, which are always replaced by new ones growing in.

Bony fish

 * Coelacanths are "living fossils". (They were thought long extinct until a live one was caught.)
 * Salmon hatch, swim to the sea, return to their birthplace by leaping up some waterfalls while trying to avoid bears, spawn, then die.
 * Flounders are so good at changing color they can blend into a chessboard.
 * A number of people die from eating fugu every year.
 * Electric eels are not really eels, but instead a species of knifefish.
 * Male clownfish actually turn female if the dominant female dies.

Amphibians

 * Amphibians have slimy skin and can "live on both land and water". (Not strictly true in the case of wholly aquatic amphibian species.)

Salamanders and kin

 * Axolotls never grow up. They do get bigger, but they retain a juvenile form (just picture an adult-sized baby).

Frogs

 * Tadpoles become frogs through metamorphosis. (Other amphibians also go through metamorphosis, but it's always frogs.) The only exception is the coqui and its relatives.
 * Frogs have slimy skin and leap. Toads have bumpy skin and hop. (Not always true, and technically it's more a matter of toads vs. other frogs, as toads are just a specialized clade of frogs.)
 * Poison-dart frogs have really deadly poison. Their bright colors warn predators to stay away. South American native tribes use their poison for hunting.
 * The cane toad is causing lots of problems in Australia.
 * The Pacific tree frog is the only frog species that actually says "ribbit."

Reptiles

 * Reptiles have dry scaly skin, are "cold blooded" (more technically, ectothermic), and lay eggs on land. (Unless you're using cladistics, in which case birds are also a specialized clade of reptiles. Not to mention that many extinct animals traditionally thought to be "reptiles" were almost certainly to some degree warm blooded.) Despite what the description of Herpetology might tell you, amphibians are not reptiles, and vice versa. Reptiles are amniotes, along with mammals and birds.

Turtles

 * You can't take a turtle out of its shell (unless you intend to rip out its ribcage and a big chunk of its backbone).
 * The leatherback turtle is the largest of all sea turtles.
 * The Galapagos tortoise is the second-largest turtle, and the largest on land.

Snakes, lizards, and kin

 * Various strange lizard defenses get a lot of attention (often the only attention these lizards will get):
 * Basilisk lizards can run on water.
 * Horned lizards spray blood from their eyes.
 * Many lizards can drop their tails as a distraction and regrow it later.
 * Blue-tongued skinks scare off predators using their blue tongues.
 * The frilled lizard spreads its frill to scare predators.
 * The marine iguana is the only marine lizard.
 * Constrictor snakes and pythons aren't venomous, they suffocate their prey.
 * The reticulated python and the anaconda are the longest and largest snake, respectively.
 * Various legless lizards aren't actually snakes.
 * The king cobra is the largest venomous snake.
 * Chameleons change color and can see in two different directions at once. They will turn white if they get startled.
 * Geckos can climb vertical surfaces.
 * This much venom from some kind of venomous snake is deadly enough to kill a huge number of people/mice.
 * The Komodo dragon is the largest living lizard. It has deadly bacteria in its mouth it can use to kill prey. (It is now known that it relies more on shock and blood loss. Also, it has actual venom in its saliva, not just bacteria.)
 * The Gila monster and beaded lizard are the only venomous lizards. Again, Science Marches On.
 * Non-venomous milk snakes and king snakes mimic venomous coral snakes.
 * Tuataras look like lizards, but they're not. They have three eyes. They're only found in New Zealand.
 * Mosasaurs were not dinosaurs.
 * Whiptail lizards are all female.

Crocodilians

 * Crocodiles have long narrow snouts, alligators have broader ones.
 * Crocodiles are able to take down HUGE prey with ease in the water.
 * A human can hold a crocodile's jaws shut without much effort, because the jaw muscles that open crocodile jaws are much weaker than those that close them.
 * Crocodilians have four-chambered hearts like mammals and birds, and some of their ancestors were likely warm-blooded (or endothermic, if you prefer)
 * Birds are their closest living relatives, as the two are the last remaining archosaur clades. It may sound strange, but they share more in common than with any other living reptile or mammal.

Dinosaurs

 * Dinosaurs are reptiles with an erect stance and "couldn't swim or fly". (The latter is clearly false now that we know birds are dinosaurs, and even some traditionally non-bird dinosaurs are now known to have been capable of flying or swimming. The swimming thing is particularly ridiculous considering that most land animals can still swim, even if they aren't specialized for it or dislike getting wet.) "Dinosaur" means "terrible lizard" (though the intended meaning was actually "fearfully great lizard").
 * We can't know what colors (prehistoric) dinosaurs were. This is no longer the case, at least for some well-preserved specimens.
 * No one knows exactly how (non-bird) dinosaurs became extinct. (In fact the K-Pg extinction is really one of the better understood mass extinctions.) They were probably killed by an asteroid impact.
 * There is a big debate about whether Tyrannosaurus is a scavenger or predator. This is actually an exaggeration as well as a false dichotomy, as only one recent researcher has endorsed the idea that Tyrannosaurus was an obligate scavenger and has now appeared to have abandoned this view, while everyone else pretty much agrees that Tyrannosaurus would have been both a scavenger and a predator as the vast majority of land carnivores are today.
 * Tyrannosaurus was the biggest carnivorous dinosaur. Now a victim of Science Marches On.
 * Oviraptor was thought to have been a specialist egg eater until it was found that the nest it was preserved on was its own, and that it was actually brooding its own nest.
 * Deinonychus may have hunted in packs.
 * Sauropods/Stegosaurus had brains the size of a golf ball/walnut. They had a "second brain" in their hip region. (The second one isn't true.)
 * Ankylosaurids could break the ankles of predators with their tail clubs.
 * Sauropods were really really big. They were the largest dinosaurs, and the largest land animals ever.
 * Giganotosaurus was larger than T. rex.

Other reptiles

 * Pterosaurs, plesiosaurs, and ichthyosaurs were not dinosaurs. Nor was Dimetrodon.
 * The largest pterosaurs (like Quetzalcoatlus) were as large as a small airplane.

Birds

 * Birds have feathers, wings, and beaks, and most can fly. (In reality this applies more to modern birds, as many extinct birds lacked beaks. Also, many dinosaurs traditionally considered non avian also had feathers and wings, and some may have even been able to fly.)
 * The peregrine falcon is the fastest animal on Earth (in a dive).
 * The spine-tailed swift is the fastest flying bird in level flight.
 * The ostrich is the largest living bird and lays the largest eggs of any living animal. No, it doesn't stick its head in the sand to avoid danger, instead it crouches close to the ground. It can run really fast, and can kill a lion with a kick. Its eyes are actually larger than its brain.
 * Cassowaries can kill you with a kick.
 * Honeyguides guide honey badgers to honey. Which is not actually true (or at least, has not actually been recorded).
 * Owls have really good hearing and can fly silently.
 * Hummingbirds can fly backwards and hover in midair.
 * The bee hummingbird is the smallest bird.
 * Galapagos finches inspired Darwin's theory of evolution. (Actually, Galapagos mockingbirds had a bigger influence.)
 * Vultures have bald heads because they eat messy food. This might not be entirely true.
 * The emu is the SECOND largest bird in the world.
 * Elephant birds laid the biggest eggs ever.
 * The harpy eagle eats monkeys and sloths. Its feet are the size of a man's hand.
 * The young hoatzin can use its wing claws to climb trees. The fact it retains wing claws is also often said to be unusual for modern birds, but this is erroneous.
 * Flamingos get their pink color from the microscopic crustaceans they eat. (This is actually the case for many brightly colored birds, though usually it's fruit or insects they eat instead.)
 * Parrots and crows are the smartest birds. They can mimic sounds (particularly human speech).
 * Archaeopteryx was the "first bird"... though this depends on its phylogenetic position and exactly what you call a bird.
 * Mandarin ducks will stop loving each other once their nest is built.
 * A canary will never find a mate if it cannot sing.

Mammals

 * Mammals have hair or fur and nurse their young with milk. Most don't lay eggs. (Not so with Mesozoic mammals, most of which were probably egg layers.)
 * The extinction of (non-bird) dinosaurs paved the way for mammals to "dominate".

Monotremes

 * There are only one/two/three/five living egg-laying mammals. (In terms of species, five is the correct number, but many works will lump all the echidnas into the same category, or at most make a distinction between long-beaked echidnas and the short-beaked echidna.)
 * The duck-billed platypus is one of the few living mammals that lay eggs. It also looks like a Mix and Match Critter. Males are venomous. They were originally thought to be a hoax.
 * Echidnas are the only other living mammals that lay eggs.

Marsupials

 * Marsupials are mammals with pouches (though some species have lost their pouches).
 * Most modern maruspials are found only in Australia. (The fact that South America actually has a lot of other marsupials as well is almost never mentioned. Some works even claim that the Virginia opossum is the only non-Australian marsupial.)
 * Opossums play dead. (Technically untrue if it's implied to be a deliberate action, as it's more of a reflex.) More specifically, it's the Virginia opossum that does this, but many works don't specify that. They are the only marsupials that live in America.
 * Opossums have prehensile tails. They're also idiots, as they have a small, simpler brain.
 * Koalas are not bears. And they eat eucalyptus leaves to get moisture. Also, they only eat eucalyptus leaves. Their appendixes are twice as long as their bodies.
 * Wombats have backward-facing pouches so they don't get soiled while burrowing.
 * The yapok is the only semi-aquatic marsupial. It can close its pouch to stop water from entering.

Hoofed mammals

 * The pronghorn is the second fastest land animal.
 * The hippo is the most dangerous mammal in Africa. It secretes a fluid from its skin that looks like blood.
 * No one knows what zebra stripes are for. No two zebras have the exact same stripes.
 * A camel's hump is filled with fat, not water.
 * The giraffe is the tallest living animal.
 * Pigs aren't actually dirty animals, and are really quite intelligent.
 * Rhinos have bad eyesight.

Carnivorans

 * The cheetah is the fastest land animal. It can go as fast as a car on a highway.
 * The honey badger is Badass.
 * The wolverine is Badass and can chase off much larger predators.
 * The tiger is the largest big cat, and one of the few which like water.
 * The jaguar is the other big cat that likes water.
 * Mongooses can fight and kill venomous snakes (usually cobras). Some savvier works will also point out that snakes aren't that much of a mongoose's diet though.
 * Hyenas aren't dogs, or pure scavengers. Their jaws can break bone. The females are dominant and have masculinized genitalia.
 * Older books will claim that the giant panda is not a bear, but closer to raccoons. We now know it is indeed a bear. It only eats bamboo. (Technically, it'll sometimes eat meat as well.)
 * If you see a cougar, back away slowly and don't try to run. The cougar is known by many names (such as mountain lion and puma).
 * The polar bear is the largest bear and non-penniped carnivoran, and is also the most predatory bear. It actually has black skin and transparent fur.
 * Lions are the only social felid. Males kill the cubs when they take over a pride.

Rodents

 * Flying squirrels don't fly, they glide.
 * Porcupines don't shoot their quills. They aren't closely related to hedgehogs.
 * Kangaroo rats don't need to drink water, they get it all from their food.
 * Rats have toxic urine. (Not true if the rat has no diseases.)

Primates

 * Lemurs are found only in Madagascar.
 * Monkeys have tails, apes don't.
 * Chimpanzees are the closest living relatives to humans. They know how to use tools.
 * Gorillas aren't actually all that aggressive.
 * Howler monkeys are really, really loud.
 * Orangutans are the largest arboreal animals

Other mammals

 * Whales are mammals, not fish.
 * The blue whale is the largest animal ever, bigger than even the largest dinosaurs.
 * The fin whale is the second largest animal ever
 * Bats are the only flying mammals. And they aren't blind, but most species do rely mostly on echolocation to find their way in the dark. Only a few species drink blood. They also don't fly into your hair.
 * Hyraxes are closely related to elephants.
 * Elephants (specifically, the African elephant) are the largest land mammals. They are also the only quadrupeds that cannot jump.
 * They are the only quadruped that cannot jump, excluding rhinos, hippos, sloths, tortoises...and in Nairobi there is an elephant jumping festival that implies that African elephants at least can jump.
 * Pangolins are the only mammals with scales.

Web Original

 * Essentially almost always averted at the Tetrapod Zoology blog, the one exception so far being basilisks.

Western Animation

 * In-universe example: in Phineas and Ferb, platypuses "don't do much".