Life on Earth can be hard. But life itself, in all its forms, is what makes this planet so unique. Organisms have adapted to thrive in some of the most inhospitable environments; places where scientists once believed it was impossible for living creatures to even exist, let alone flourish.
In every corner of the planet, whether it is a mile below the surface of the ocean completely out of reach of the sun, or right in our backyard, life—as the beloved "Jurassic Park" mathematician Dr. Ian Malcolm would say—finds a way. And for the luckiest on Earth, their lives may even be narrated by the great David Attenborough.
The BBC’s Natural History Unit has produced 150 documentaries since 1957 with more on the horizon. Over the past 20 years especially, advances in technology have allowed documentary filmmakers to give audiences unprecedented perspectives of the natural world. Released in 2006 after five years in the making, "Planet Earth" was the first nature documentary shot in high definition.
Ten years later, the sequel, "Planet Earth II," became the first shot in ultra-high definition. These are just two of many documentaries that introduced us, in stunning detail, to the unknown worlds within our own.
Flora and fauna never before seen made their debuts on film. Things we thought were familiar revealed themselves to be surprising when observed from a new vantage point. What these films have done best is to show us the staggering scope, complexity, and interconnectedness of nature. Stacker wanted to highlight just a few examples of these unexpected revelations from some of the most popular nature documentaries over the past two decades.
What does rare mean in this context? We watched every episode of "Blue Planet I," "Blue Planet II," "Planet Earth I," "Planet Earth II," "Life," "Africa," and "Our Planet," and pulled out examples of unique occurrences in the natural world. Rare includes animals not often seen, animals with extreme survival tactics, those with small geographic distribution, and those with remarkable evolutionary adaptations.
Read on for a sampling of some of these rare and spectacular animals.
Monarch butterflies
- Documentary featuring this animal: "Life: Insects"
While monarch butterflies are common, their migration is exceedingly mysterious. Each year, monarchs travel more than 3,000 miles from Canada to a small patch of Oyamel fir trees in the mountains of Mexico before the winter temperatures set in. Exactly how they find their way to this bit of forest is still unknown.
The monarchs gather by the millions in the branches of the Oyamel firs, which create a climate optimal for hibernation. The roundtrip journey is completed throughout several generations with one “super generation” that makes the entire trip south, hibernates, starts the return journey, and breeds the next generation all in eight months. What makes this so extraordinary is that every other generation lives between five and seven weeks to complete their leg of the return trip back to Canada.
Amazon river dolphin
- Documentary featuring this animal: "Planet Earth II: Jungles"
The Amazon river dolphin, also known as the boto, is a freshwater dolphin that lives in the Amazon River basin and spends the wet season swimming deep among the trees when the river floods the rainforest floor. Although no consensus has been reached within the scientific community on how exactly these dolphins made the biogeographic leap from ocean to river, some experts believe they branched off from their more familiar marine relatives roughly 15 million years ago during retreating sea levels of the Miocene epoch. Since then, adaptations like long narrow snouts for hunting, unfused vertebrae allowing them to bend to 90-degree angles, and refined echolocation have made these river mammals adept hunters among the flooded tributaries of the Amazon rainforest.
Railroad worms
- Documentary featuring this animal: "Planet Earth II: Jungles"
Railroad worms are some of the most specialized hunters on the planet. These worms, named for their resemblance to lighted windows on a passenger train, are actually poisonous beetles that look like caterpillars. Females produce a bioluminescent glow caused by a chemical reaction between the molecule luciferin and the enzyme luciferase; it’s the same reaction that gives fireflies their signature glow. These lights serve as a warning to other predators to stay away. Certain species of railroad worms are also equipped with a red bioluminescent light on top of their heads, which they can turn on and off. Many insects, like millipedes, can’t see red light, giving the railroad worm a distinct advantage in the dark.
New Zealand glow worms
- Documentary featuring this animal: "Planet Earth I: Caves"
Like the railroad worm, these insects aren’t actually worms at all, but a variety of beetle. Few bioluminescent displays in nature are quite as mesmerizing as that of a cave ceiling full of blue lights from the Arachnocampa luminosa, also known as the New Zealand glow worm. Deployed primarily as a hunting tactic, the light of the glow worm emitted from its lower abdomen is used to attract insects and ensnare them in beaded strings of slime the glow worm also produces.
The insect uses digestive saliva to liquefy and subsequently suck out the inside of its prey. Only females have the ability to glow. The glow worm’s light is also one of the few examples in nature of the female in a species using ornamentation to attract a mate. Scientists are unsure what advantage this provides to female glow worms.
Deep-sea hatchetfish
- Documentary featuring this animal: "Blue Planet II: The Deep"
Life in the deep is mostly a game of deception. Many deep-sea species are equipped with highly specialized bodies made for evading predators. But predators have special adaptations, too. Take the deep-sea hatchetfish, for example. Predators of the hatchetfish distinguish their prey by looking up, locating their silhouettes against the backdrop of what little light filters down from above.
Hatchetfish have rows of photophores, or light-producing cells, in their translucent bellies, which they can use to exactly match the color of the light filtering down. This makes them almost invisible from below. It would seem to be a perfect evolutionary adaptation. But Mother Nature always seems to have the checkmate ready. It has been discovered that predators of the hatchetfish have eyes that can distinguish between light produced by photophores and light produced by the sun.
Velvet worms
- Documentary featuring this animal: "Our Planet: Jungles"
Velvet worms are some of the oldest and most bizarre living creatures on the planet. They’ve existed, almost entirely unchanged, for over 500 million years; that’s long enough to see dinosaurs come and go. Most species of velvet worms are found in moist tropical or coastal areas and feed on other small invertebrates. And their preferred method of hunting? Rapid-firing swinging jets of immobilizing slime, followed by an injection of digestive saliva that liquefies their prey.
Philippine eagle
- Documentary featuring this animal: "Our Planet: Jungles"
The critically endangered Philippine eagle, found only on four islands in the Philippines, is one of the rarest birds on Earth. Loss of their natural forest habitat due to commercial logging has reduced their numbers to fewer than 400 globally. Conservation efforts include researching and monitoring the current populations, as well as enforcing laws around habitat management.
After their initial discovery in the late 19th century, they were commonly referred to as “monkey-eating eagles” because it was believed their diet consisted exclusively of monkeys. It has since been discovered that Philippine eagles feed on a variety of prey. It is estimated that these eagles can live between 30 and 60 years and can reach heights of over 3 feet with wingspans of 7 feet, making them some of the largest birds of prey in the world.
Gulper eels
- Documentary featuring this animal: "Blue Planet II: The Deep"
Gulper eels, like many of their deep-sea neighbours, look like the stuff of science fiction. Life at extreme depths—over a mile down—has led to extreme biological adaptations for the survival of marine species. For the gulper eel, this means an enormous mouth to capitalize on any infrequent prey that swims by, regardless of size, attached to a meter-long tail with a bulb at the bottom, which acts as a lure. The gulper eels’ large mouths—large enough to swallow prey as big as the eels themselves—have earned them the nicknames “pelican eels” and “umbrella-mouth gulpers.”
Birds of paradise
- Documentary featuring this animal: "Our Planet: Jungles," "Planet Earth I: Pole-to-Pole"
When it comes to courtship, you would be hard-pressed to find a species more dedicated or more exuberant than the bird of paradise. There are over 40 species of birds of paradise, each with their own unique courtship rituals and striking plumage. It is the male birds of paradise that sport elaborate ornamentation, like streamers or bright breast feathers, to attract a mate. But what’s a costume without a performance? Males also dance, showing off their colors and shifting their bodies into various shapes, making them almost unrecognizable as birds.
Snow leopards
- Documentary featuring this animal: "Planet Earth II: Mountains"
Sometimes referred to as “ghost cats” because of their elusive nature, snow leopards are extremely rare. Little is known about their lives in the mountains of Central Asia, and because there is so little prey to sustain large populations, there are only around four snow leopards per 40 square miles. It wasn’t until 1971 that the first image of a snow leopard in the wild was captured by biologist George Schaller. Even today, capturing them on film requires meticulous tracking, motion sensors, infrared technology, and an abundance of patience.
Trogolobites
- Documentary featuring this animal: "Planet Earth I: Caves"
Troglobites are all animals that have adapted to life in caves. They spend their entire lives in these dark subterranean environments and, over thousands of years, have lost their eyes and skin pigmentation as a result. Some troglobites are hyperspecialized, like cave angelfish, whose entire population lives only in the waterfalls inside two caves in Thailand. Texas cave salamanders and Belizean white crabs are two more examples of troglobites who live only in one cave system.
Pygmy sloths
- Documentary featuring this animal: "Planet Earth II: Islands"
Pygmy three-toed sloths are a critically endangered species of sloth found only on a remote island called Isla Escudo de Veraguas off the coast of Panama. Their entire natural habitat is roughly the size of New York City’s Central Park. This has resulted in a process called insular dwarfism, or island dwarfism—when a species shrinks over generations in response to the limited resources of an island environment. At the time of filming, only a few hundred sloths remained in the wild; conservation efforts have received little attention.
Chinstrap penguins of Zavodovski Island
- Documentary featuring this animal: "Planet Earth II: Islands," "Blue Planet: Frozen Seas"
Zavodovski Island in the Southern Ocean is home to one of the largest penguin colonies on Earth: over 1 million pairs of mating chinstrap penguins. But it’s not exactly paradise by our standards—Zavodoski Island is an active volcano in the middle of some of the roughest, stormiest seas on the planet. This presents unique advantages and challenges for its residents.
The heat emanating from the volcano means the ground is warm, with little snow or ice buildup, optimal for rearing young. But hunting for food in the waters surrounding the island means treacherous descents down cliffs, as well as powerful breaking waves that beat against the rockface which serves as an entry point for the penguins. Not to mention the constant, potentially devastating risk of a volcanic eruption.
Stalk-eyed fly
- Documentary featuring this animal: "Life: Challenges of Life"
Body modification isn’t unique to our species. Male stalk-eyed flies use a sort of body modification to attract mates. They take in air bubbles and push them up into their heads and into their eyestalks. Each bubble of air elongates the eyestalks horizontally. The wider apart their eyes are positioned, the more dominant the male is perceived to be. The most dominant male wins the right to mate with all the female stalk-eyed flies in his territory.
Giant Pacific octopus
- Documentary featuring this animal: "Life: Challenges of Life"
Giant Pacific octopuses exhibit one of the greatest displays of parental devotion in nature. After a female has laid her eggs in a carefully chosen den, she will spend the rest of her life tending to them. Keeping them free of algae build-up and safe from predators, she will not leave them, even temporarily, in order to feed. After six months of protecting and tending to her clutch, she usually dies of starvation.
Rock pythons
- Documentary featuring this animal: "Africa: Congo"
Like the giant Pacific octopus, the female rock python exhibits enormously selfless acts of devotion in the service of its young. A mother python will heat her body in a shaft of sunlight until her temperature reaches a dangerously high 105 degrees Fahrenheit. She’ll then retreat back to her burrow and wrap her body around her clutch of eggs, transferring that heat and ensuring their temperature remains above 86 degrees Fahrenheit. This threshold is critical to their development. She will do this every day for three months until they hatch. If the stress on her body doesn’t kill her, it could take the mother up to three years to fully recover.
Chemical-firing insects
- Documentary featuring this animal: "Life: Insects"
Insects like European wood ants and devil rider stick insects have developed relatively painful defense mechanisms to deter predators. These are just a few examples of insects that produce chemical sprays. But none is as extreme as the bombardier beetle, which houses two reservoirs in its abdomen: one filled with hydrogen peroxide and hydroquinones, and another filled with peroxidase and catalase. When separated, the mixtures are innocuous. But when mixed together, the result is a violent reaction. When threatened, the bombardier beetle will open the valve separating the two, resulting in an explosive chemical process. The beetle can aim and fire (out of its backside) over 500 times per second and the liquid can get as hot as 212 degrees Fahrenheit.
Sword-billed hummingbirds
- Documentary featuring this animal: "Planet Earth II: Jungles"
Sword-billed hummingbirds have evolved to fill a niche in their environments—one that exempts them from competition over limited resources with other species. The sword-billed hummingbird is the only bird with a beak longer than its body. This elongated beak enables the unusual hummingbird to reach nectar deep inside flower shafts that other birds cannot access.
Pompeii worms
- Documentary featuring this animal: "Blue Planet II: The Deep"
Pompeii worms are among the rarest and most resilient creatures on the planet. They belong to a group of organisms classified as extremophiles—lifeforms that thrive in the most extreme conditions. That’s because they are found in hydrothermal vents steeped in hydrogen sulfide along the mid-ocean ridge. Pompeii worms can survive in temperatures up to 176 degrees Fahrenheit, higher than any other animal on Earth has been known to withstand. These worms, along with other newly discovered life forms found in the complete darkness of the mid-ocean ridge, overturned the belief that all life on Earth was dependent upon the sun.
