Facts about animals
Animals are the easiest place to find facts that sound invented. Three hearts, blue blood, cube-shaped droppings, a punch fast enough to boil water for an instant — every one of these is ordinary biology to the animal doing it. The collection here leans on well-documented behaviour and anatomy rather than folklore, so each entry comes with a short explanation of why the trick actually works and a source you can read next.
Octopuses have three hearts and blue blood.
Two of the hearts pump blood through the gills, while the third sends it around the rest of the body. When an octopus swims, the body heart actually stops beating, which is one reason they prefer to crawl.
A mantis shrimp punches so fast that the water around its club briefly boils.
Some mantis shrimp strike with club-like limbs that accelerate faster than a .22 bullet. The blow is so quick that it creates cavitation bubbles, which collapse with a flash of heat and light.
Tardigrades have survived being exposed to the vacuum of space.
In 2007, dried tardigrades were flown into orbit and exposed to open space for ten days. Back on Earth, many of them revived and even reproduced.
One jellyfish can age backwards, turning itself back into a polyp.
Turritopsis dohrnii, the so-called immortal jellyfish, can respond to injury or starvation by reverting from its adult form to a juvenile polyp. The polyp then grows into new jellyfish all over again.
Sharks have been around longer than trees.
Shark-like fish appear in the fossil record around 450 million years ago. The first true trees, such as Archaeopteris, showed up roughly 385 million years ago.
Crows recognise individual human faces and can hold a grudge for years.
Researchers in Seattle wore a mask while trapping and tagging crows. Years later, crows still scolded and mobbed anyone wearing that mask, including birds that had never been trapped themselves.
In 1932, Australia sent soldiers with machine guns to fight emus, and the emus won.
Around 20,000 emus were trampling wheat fields in Western Australia, so the army was called in. After weeks of chasing birds that scattered and outran trucks, the operation was abandoned with only a small fraction of the emus killed.
Axolotls can regrow lost limbs, and even parts of their heart and brain.
If an axolotl loses a leg, it grows a complete new one with bones, muscles and nerves, without scarring. The same works for the tail, the spinal cord and pieces of the heart and brain.
Greenland sharks can live for around 400 years, longer than any other vertebrate.
A 2016 study dated the eye lenses of Greenland sharks with radiocarbon and estimated that the largest female was roughly 390 years old. Some sharks swimming today were probably born before the year 1700.
Honeybees tell each other where flowers are by dancing.
A returning forager performs a figure-of-eight waggle dance on the honeycomb. The angle of the dance shows the direction relative to the sun, and the length of the waggle tells the distance.
Flamingos are born grey; their food turns them pink.
Chicks hatch with grey or white feathers. The pink and orange colours come from carotenoid pigments in the algae and small crustaceans that flamingos filter out of the water.
The blue whale is the largest animal that has ever lived, and its heart weighs as much as a small car.
Blue whales reach about 30 metres and can weigh close to 200 tonnes, heavier than any known dinosaur. A blue whale heart weighs roughly 180 kilograms.
Wombats are the only animals known to produce cube-shaped droppings.
A wombat can leave dozens of small, almost perfectly cubic droppings in a night, often stacked on rocks and logs. The cubes do not roll away, which helps mark territory.
Hummingbirds are the only birds that can fly backwards.
They can hover in place, fly sideways and reverse out of a flower. Some species beat their wings more than 50 times per second while doing it.
A pistol shrimp snaps its claw so fast that the bubble it creates is briefly hotter than the surface of the Sun.
The snap fires a jet of water that forms a cavitation bubble. When the bubble collapses it produces a bang of over 200 decibels, a flash of light and a temperature of several thousand degrees for a split second.