Animals

Wild yak (Bos mutus): description, habitat, behavior and conservation Wild yak The wild yak (Bos mutus) is a large high‑altitude bovid native to the Tibetan Plateau and Himalayas. This article covers its appearance, ecology, relationship with domestic yak, th…

Wildebeest (Gnu): overview, behavior, and conservation Wildebeest Wildebeest (gnus) are two species of large African antelope known for mass migrations, grazing ecology, and importance to savanna food webs. This article surveys their biology, beh…

Willow grouse (willow ptarmigan) — Lagopus lagopus Willow grouse A northern gamebird of the genus Lagopus found across Arctic and subarctic Eurasia and North America, noted for seasonal white winter plumage and importance in tundra ecosystems an…

Wilson's bird-of-paradise A small, vividly colored bird-of-paradise endemic to a few Indonesian islands; noted for the male's ornate plumage, elaborate courtship displays, and conservation importance.

Wing: structure and function in animals and aircraft Wing A wing is a surface that produces lift for flight. This article explains biological and aircraft wings, their parts, how they generate lift, historical development, uses, and notab…

Winghead shark (Eusphyra blochii) Winghead shark A small hammerhead shark notable for an exceptionally wide cephalofoil. Found in tropical Indo-Pacific coastal waters, it is fished locally and faces pressure from fisheries and ha…

Wintonotitan Wintonotitan is a genus of large sauropod (titanosauriform) known from Early Cretaceous rocks in Australia. It is represented by partial skeleton remains that inform regional sauro…

Wisent (European bison) Wisent The wisent or European bison (Bison bonasus) is Europe’s largest wild land mammal. This article covers its appearance, distribution, conservation history, ecology, and differences…

Witchetty grub: larval insect, cultural food, and natural history Witchetty grub Witchetty grub is the large, edible white larva of several Australian moths, most famously Endoxyla leucomochla. Important in Aboriginal diets, it has distinctive biology, cultural…

Wiwaxia: Cambrian sclerite-bearing animal from the Burgess Shale Wiwaxia Wiwaxia is an extinct, soft-bodied Cambrian animal known from Burgess Shale fossils. It bore overlapping scales and defensive spines, grazed on seafloor microbial mats, and its rel…

Wolf (Canis lupus): biology, behavior, and relationship with humans Wolf An overview of the grey wolf (Canis lupus): taxonomy, appearance, behavior, range, subspecies, conservation status, and its role in dog domestication and human culture.

Wolf spider (Lycosidae): biology, behavior, and human interactions Wolf spider Wolf spiders (family Lycosidae) are ground-dwelling hunting spiders known for maternal care, active stalking behavior, and a wide range of sizes and habitats worldwide.

Wolterstorffina — a genus of African true toads Wolterstorffina Wolterstorffina is a small genus of true toads (family Bufonidae) found in parts of Nigeria and Cameroon. These amphibians are terrestrial, often linked to moist forest and montane…

Wolverine (Gulo gulo) — large northern mustelid Wolverine Wolverine (Gulo gulo) is the largest mustelid: a solitary, muscular carnivore and scavenger of circumpolar regions, notable for thick fur, wide-ranging habits and adaptations to co…

Wombat Short, stocky marsupials native to Australia known for burrowing, backward-facing pouches and distinctive cube-shaped feces; three living species occur in two genera with varied co…

Wonder Pets! — preschool animated series about teamwork and rescue Wonder Pets Wonder Pets! is an American preschool series featuring Linny, Tuck and Ming-Ming, using musical storytelling and photo-puppetry to teach cooperation, problem solving and empathy.

Wood frog (Rana sylvatica): description, habitat, and life cycle Wood frog The wood frog (Rana sylvatica) is a widespread North American amphibian known for its early spring breeding and exceptional tolerance of freezing during winter.

Wood mouse (Apodemus sylvaticus) Wood mouse A small wild rodent native to Europe and nearby regions, the wood mouse is a nocturnal, seed-eating mammal important as a seed disperser and prey species; common and not globally t…

Woodland dormouse (Graphiurus murinus) Woodland dormouse Small nocturnal dormouse species native to South Africa. Arboreal and omnivorous, known as the African dwarf or pygmy dormouse; sometimes kept as pets but requires specialized care…

Woodpecker (Picidae): characteristics, behavior, taxonomy and conservation Woodpecker Woodpeckers (family Picidae) are specialized near-passerine birds that forage and excavate in wood. This article summarizes their anatomy, behaviour, distribution, classification a…

Woodpecker finch A Galápagos finch famed for using tools — probing tree bark with twigs or cactus spines to extract insect larvae — an important example of animal problem-solving and ecological ada…

Woodward's wallaroo (Macropus bernardus) Woodward's wallaroo Overview of Woodward's wallaroo, a small rock-dwelling macropod of Arnhem Land, covering appearance, behaviour, habitat, and conservation concerns.

Woolly dormouse (Dryomys laniger) Woolly dormouse A small, nocturnal rodent of the Gliridae family endemic to Turkey. Known for its dense fur and arboreal habits, it occupies forested habitats and requires further study for clear…

Woolly mammoth (Mammuthus primigenius) — Ice Age elephant Woolly mammoth Extinct Ice Age elephant adapted to cold steppe‑tundra. Known from bones and frozen carcasses across northern Eurasia and North America; hunted by humans and studied through paleon…

Woolly monkey Woolly monkeys are large New World primates with thick fur and prehensile tails, native to Amazonian forests in South America; they are social, mainly frugivorous, and several spec…

Woolly rhinoceros (Coelodonta antiquitatis): Ice Age megaherbivore Woolly rhinoceros Extinct Ice Age rhinoceros that roamed the mammoth steppe of northern Eurasia. Known from fossils, cave art and permafrost-preserved carcasses; extinction linked to climate change…

Working dog A working dog is bred or trained to perform practical tasks that assist people — from herding and guarding to search and rescue, hunting, and other specialized roles.

Worms: diversity, biology, and relationships with humans Worm A general overview of worms: their body plans, major groups, ecological roles, medical importance, and common non-worm uses and misconceptions.

Wrasse (family Labridae): colourful reef fishes and their biology Wrasse Wrasses (Labridae) are a diverse family of mostly small, often brightly coloured marine fishes found in reefs worldwide; they show varied feeding strategies, sex change and key eco…

Wren (Troglodytidae): small, vocal passerine birds Wren Wrens are small, energetic passerines of the family Troglodytidae, mainly New World in distribution. Known for cocked tails and loud songs, about 80 species occupy varied habitats…

Wuerhosaurus Wuerhosaurus is a genus of Early Cretaceous stegosaurid from China, noted for broad hips, rounded dorsal plates and its role as one of the latest-known stegosaurs.

Xenarthra: the armadillos, sloths, and anteaters of the Americas Xenarthra Xenarthra is a distinctive superorder of placental mammals native to the Americas, including armadillos, sloths and anteaters; notable for unique vertebral joints, low metabolic ra…

Xenopus: African clawed frogs and their role in research and ecology Xenopus Xenopus is a genus of African aquatic frogs known for fully webbed toes and laboratory importance; includes species such as X. laevis and X. tropicalis and notable polyploidy.

Xiaosaurus — small mid-Jurassic ornithischian dinosaur Xiaosaurus Xiaosaurus is a small, bipedal herbivorous dinosaur from mid‑Jurassic China (about 169–163 Ma). Known from fragmentary fossils, it helps illuminate early ornithischian anatomy and…

Xiaotingia — a small feathered theropod from the Jurassic of China Xiaotingia Xiaotingia is a small, feathered theropod genus from Late Jurassic Liaoning, China, notable for a 2011 analysis that allied it with Archaeopteryx and raised questions about early b…

Xiphactinus — Large predatory fish of the Late Cretaceous seas Xiphactinus Xiphactinus was a large, fast-swimming predatory bony fish from the Late Cretaceous Western Interior Seaway, known from dramatic fossil specimens and wide geographic fossil occurre…

Xiphosura: horseshoe crabs and their extinct relatives Xiphosura Xiphosura is an order of marine chelicerates that includes living horseshoe crabs and many extinct relatives. This article covers their anatomy, fossil record, classification, ecol…

Yangchuanosaurus: a large Jurassic carnosaur from Sichuan, China Yangchuanosaurus Yangchuanosaurus is a genus of large Jurassic carnivorous dinosaur from Sichuan, China, known from several skulls and skeletons; notable for cranial ornamentation, long tail, and r…

Yellow-bellied glider (Petaurus australis) Yellow-bellied glider A medium-sized nocturnal gliding marsupial of eastern Australia that lives in tall eucalypt forests, feeds on sap and nectar, and faces habitat-related conservation concerns.

Yellow-billed magpie (Pica nuttalli) Yellow-billed magpie Overview of the yellow-billed magpie, a California endemic songbird: appearance, behavior, taxonomy, breeding, threats and conservation status.

Yellow-eyed penguin (Megadyptes antipodes): description, behaviour and conservation Yellow-eyed penguin The yellow-eyed penguin (Megadyptes antipodes), or hoiho, is an endangered, distinctive New Zealand penguin known for yellow head stripes, solitary nesting, coastal foraging and co…

Yellow-lipped sea krait (Laticauda colubrina) Yellow-lipped sea krait A venomous, semi-aquatic sea snake of the Indo-Pacific distinguished by a yellow upper lip and black-and-white bands. It forages in reefs, returns to land to lay eggs, and faces ha…

Yellowfin tuna (Thunnus albacares) Yellowfin tuna A large, fast-swimming tropical tuna species valued by commercial and sport fisheries; known as ahi in many markets and recognized by its bright yellow fins.

Yellowjacket: biology, behavior, and interactions with people Yellowjacket Yellowjackets are social wasps (genera Vespula and Dolichovespula) known for black-and-yellow markings, complex colonies, predatory larvae diets, and frequent encounters with human…

Yi (dinosaur) — a small Jurassic climber with membranous gliding wings Yi (dinosaur) Yi is a small, tree‑associated theropod from the Jurassic of China notable for a unique wrist bone and skin membrane that supported a bat‑like gliding surface.

Yorkshire Terrier (Yorkie) Yorkshire Terrier Small, long-coated terrier from Yorkshire, England. Bred for rodent control, now a popular companion breed known for silky hair, bold temperament, and specific grooming and health…

Yutyrannus — large feathered tyrannosauroid of the Early Cretaceous Yutyrannus Yutyrannus huali, a large Early Cretaceous tyrannosauroid from northeastern China, is the largest dinosaur known from direct feather impressions; its fossils illuminate integument,…

Zalmoxes — a Late Cretaceous ornithopod from the Hateg region Zalmoxes Zalmoxes is a genus of small to medium ornithopod dinosaur from the Late Cretaceous Hateg Basin in present-day Romania, notable for its place in island faunas and for relatively co…