The Kauaʻi cave wolf spider has adapted to the lightless caverns of southern Kauaʻi by losing its eyes entirely. It creeps slowly — consuming ~40% as much oxygen as surface-dwelling wolf spiders — pursuing its primary prey: the Kauaʻi cave amphipod, a blind crustacean endemic to the same caves.

The raccoon dog isn’t a raccoon at all — it’s a canid, more closely related to foxes. It’s the only member of the dog family that hibernates and one of the few to use communal latrines, where it leaves behind smelly “messages” about its diet, health, and breeding status for other raccoon dogs to sniff out.

The white-tipped sicklebill uses its extremely decurved bill to reach inside sharply curved flowers, allowing it to drink nectar other nectarivores cannot reach. It is also a ‘trapliner’ — repeating the same foraging circuits, visiting favourite flowers along its particular route.

The immortal jellyfish is so-called because it can revert to a previous stage in its life cycle due to stress or injury. However, this isn't immortality as we typically think of it: the jelly turns back into a stationary polyp that spawns several genetically identical medusae.

The Kangaroo Island dunnart lives only on Kangaroo Island, off South Australia. In 2019–2020, catastrophic bushfires swept across the island, burning over 90% of the dunnart’s habitat. The species was feared extinct, but a few were found to have survived — perhaps just 50–100 individuals.

The eastern and western meadowlarks look nearly identical, behave in the same way, and share similar habitats — even overlapping in range in the central plains of North America — yet they are separate species that rarely interbreed. What keeps them apart are the different songs they sing.

The male Darwin’s frog “swallows” his offspring — nudging the eggs into his vocal sac — where they soon hatch into tadpoles. He carries them for 50 to 70 days, during which they develop entirely within the sac, before spewing out fully formed froglets.

The pygmy hog is the smallest pig species in the world — standing just 25 centimetres (9.8 in) at the shoulder. It is also one of the rarest. Once widespread across the southern foothills of the Himalayas, fewer than 250 mature individuals now survive, confined to a small patch of grassland in Assam, India. 

Each spring, thousands of firefly squid gather in Japan’s Toyama Bay and light up the water with their neon-blue bioluminescence. After laying and fertilising their eggs, they die. A year later, their offspring will return to do the same.

The Asian koel is a brood parasite that lays its eggs in the nests of other birds. The species is also sexually dimorphic: males are dark-feathered goths, while females are boldly streaked in brown and white.

The pig-nosed turtle is the sole surviving species in its family. It lives in the rivers of northern Australia and southern New Guinea, using its pig-like nose to "snorkel" without exposing the rest of its body.

The saola — often called the "Asian unicorn" — is endemic to the Annamite Mountains of Laos and Vietnam. Discovered by science in 1992, it has never been directly observed alive by researchers in the wild and may number fewer than 100 individuals.

The capuchinbird is named for its resemblance to Capuchin monks, with the brown plumage around its bald head looking like the monks’ hooded robes.

Rainbow lorikeets travel in nomadic flocks, following the flowering of trees — using their brush-tipped tongues to feed on nectar and pollen. At night, they roost communally, perching close together and occasionally hanging upside down or lying on their backs, feet in the air.

The Bawean hog deer is the rarest deer in the world. It's only found on the small Indonesian island of Bawean and is considered 'critically endangered' — with an estimated population of fewer than 300 individuals.

The bald parrot is a species that lacks any head feathers — apart from some sparse bristles. Endemic to the east-central Amazon, its baldness might be an adaptation for eating fruit without getting its feathers sticky.

The Chacoan peccary was initially described as an extinct species from fossils discovered in 1930. In the early 1970s, a living population was found in an isolated area of Paraguay — in a region known as the Gran Chaco. This species is the largest and rarest of the three living peccaries.

The central rock rat lives in central Australia around and among rocks — sheltering in crevices during days that can reach a blistering 50°C (122°F). Threatened by bushfires and invasive predators, its range has shrunk by around 95%.

A paradox frog tadpole can grow to be 27 centimetres (11 in) long — the largest tadpole of any frog. It eventually metamorphoses into a shrunken adult frog, only some 7 centimetres (2.7 in) long.

Madame Berthe's mouse lemur is the smallest primate in the world. On average, it measures 10 centimetres (3.9 in) plus a 13-centimetre (5-in) tail and weighs just 33 grams (1.2 oz) — lighter than a golf ball.