30 Outstanding Animals that Start with O (With Pictures)

Animals that Start with O

What! A list of animals starting with O you ask? Owl. Octopus. Ostrich. Oh, that’s all?

This list will take you on an animal adventure from the smallest to the largest animals in the world all of them beginning with the letter O.

The conversation started when one of my colleagues said she liked octopuses and I mentioned they can be quite dangerous if provoked, particularly the blue-ring variety. That led to a discussion about animals that start with O and here’s the list we came up with. 




A member of the weasel family, this cute but dangerous animal is a carnivorous mammal that can be sighted either on land or at sea. They are found both in saltwater and freshwater

Not many know this, but otters have the thickest skin in the animal kingdom.

Otters are today classified as endangered. They have been historically hunted for their fur, pushing them to the point of extinction. Though their population has revived significantly in comparison, most of the species face a great threat of habitat loss today.

There are 13 species of otters currently surviving and together make up the subfamily Lutrinae.

With strong tails and webbed feet, otters are exceptional swimmers. Giant otters can swim up to 14.4 kph – faster than most penguins!

An endearing fact about otters is that they hold hands as they sleep, floating on their back – adorable, right?

Somewhat bizarre ritual otters have been performing are ‘scat dances’ before pooping. They’re especially notorious for smelly droppings, a not-so-cute fact.


Ornate chorus frog

Ornate chorus frog

The ornate chorus frog is a small, distinctly colorful, and rarely seen chorus frog species. It is most commonly found in the Southern coastal plain of Southeastern United States.

Colors ranging from metallic silver-brown, reddish-brown, black, and bright green, the most distinctive feature of the ornate chorus frog is a dark stripe through the eye. Their tadpoles are also remarkably peculiar to most frogs’.

Like most frogs, this species is nocturnal.

With a notable decline in the last decade, the ornate chorus frog is classified as a threatened species. They are a rare sight and are mostly seen during the winter and often remain underground throughout early fall and summer.




The Olm is a blind cave salamander and a fascinating deep-sea creature that lives in complete isolation. Olms are native to central and southeastern Europe.

This strange-looking amphibian has a distinctly elongated body and underdeveloped limbs. With an average size of 8-12 inches, the females are usually larger than the males.

A creature found only in caves, Olms have evolved to become completely blind due to their adaptability to life in deep, dark caves. Because of its dark natural habitat, it can detect the presence of light through its skin.

It’s the only vertebrate to live the entire length of its life in a cave!

The olm is often described as human fish and a baby dragon because of its long, snake-like body with pale pinkish skin.

Interestingly, when kept in the cave’s darkness for a long time, their skin color changes to black and reverts back to pink or white when out.

The fact that this creature is most known for is its especially long life span. Olms can live for more than 100 years! How? It’s a mystery that is still unsolved.


Oliver Ridley Sea Turtle

Oliver Ridley Sea Turtle

Named after their generally greenish color, Oliver Ridley Sea Turtles are the most abundantly found sea turtles. They are also the smallest among all sea turtles, with only 2 feet of shell height and 100 pounds in weight.

This species is omnivorous, usually feeding on seaweed, shrimp, snails, jellyfish, and algae.

The Oliver turtles face a serious threat and are declared protected in many countries.

Like most sea turtles, Oliver turtles also have a synchronized nesting behavior called ‘natal homing.’ They travel thousands of miles and arrive at specific shores to breed together. Adult Oliver turtles are sexually dimorphic.

Their natural habitat is warm, tropical waters and are most commonly found in the tropical regions of the Atlantic, Indian and Pacific oceans. However, they nest all over the world.


 Aquatic animals 



Octopuses are eight-legged sea creatures that are found everywhere across the world. O.vulgaris is the most common type of octopus.

One of the most venomous animals globally, the venom ejected from an angry or scared octopus can kill adult humans within minutes by first paralyzing the body.

Though they are venomous, octopuses are part of many cuisines, mostly consumed in east Asian cultures.

Among the entirety of the invertebrate family, octopuses are the most intelligent of all.

The most commonly known fact about this animal is its insane camouflaging ability. A lesser-known fact is its ability to lift up to 16 kgs with each sucker on a single tentacle! Octopuses can also regrow their tentacles if severed.

Another lesser-known fact about these creatures is that male octopuses die after mating.

Solitary by nature, octopuses usually stick to the ocean floor and live in small corners or dens; they build these ‘houses’ themselves using rocks and other ocean junk.  They can sometimes even build underwater ‘cities’! One such city was found in 2009.




Oysters have been around for almost 180 million years or so – they were a staple in the Neolithic man’s diet.

At first glance, it may look like they’re just a hard shell, but oysters have eyes all over their bodies. Their diet is limited to only sea plankton.

A single oyster can filter as little as 1.5 gallons to an astonishing 50 gallons of water in a day in search of food.

A surprising fact you might’ve not known is that oyster reefs act as natural barriers to strong storm waves and can help avoid flooding, reduce erosion and damage from coastal storms.

They are also largely believed to be aphrodisiacs due to their ability to increase human stamina and testosterone production in males.

Also, there’s a good possibility that an oyster is very much alive as you’re eating it.

Oysters produce pearls when small amounts of trapped sand or other irritants are accumulated inside over time.

Finally, oysters can change their sex, more than once in fact.




Oscars are a common freshwater aquarium species belonging to the cichlid family.

Oscars are originally native to the Amazon basin. Naturally co-existing with piranhas in the wild, no wonder they are highly aggressive and difficult to keep. 

Known to be extremely aggressive, the Oscar fish is one of the most intelligent aquarium fish species. A testimony to their intelligence, these fish can recognize their owners and also be trained to do tricks! They are also very notoriously known for eating their tank mates.

A wild adult Oscar fish can grow up to 18 inches, while domesticated grow up to 12 inches.

This fish requires certain conditions to survive and remain healthy. Warm temperature – about 77 degrees – and a constant need for vitamin C are two such requirements.

They are usually dark, almost black in color with orange marbling, with no distinct difference between the two sexes except for their genital papilla.

If threatened or when sensing danger, Oscars can play dead.


Ocellaris clownfish

Ocellaris clownfish

Also known as common clownfish, the ocellaris clownfish is a very peaceful and communal fish in general. They’re one of the most commonly kept aquarium fish species.

Nemo and Marlin are Ocellaris clownfishes.

Commonly found in the Pacific and Indian ocean reefs, this fish species is very nestled and hardly stray more than a few meters from its nests.

All Ocellaris clownfish are born male and are hermaphrodites, meaning they can change sex to turn female.

A clownfish school is led by the most aggressive female in the group, and in the event of their death, the next biggest male will turn himself and take over.

Contrary to martin’s over-protectiveness over Nemo, once hatched, clownfish babies are left on their own by their parents.


Ocellated puffer fish

Ocellated puffer fish

Also known as Emerald puffer and common puffer, is a rather aggressive and highly predatory puffer species and is best kept alone if kept in captivity.

The ocellated pufferfish is found in tropical waters. It is native to South Asia, i.e., India, Sri Lanka, Bangladesh, and the Malay Archipelago. They like to stay hidden under rocks and in corners and avoid contact with other fish except for when they’re hunting for food.

Unlike other fish, pufferfish are absolutely scaleless. They aren’t the best swimmers. Their slow, uncoordinated gait makes them quite vulnerable to predators.

Pufferfish aren’t venomous but highly toxic. The concentrated toxins released from a single pufferfish’s skin are about 1,200 times stronger than cyanide and can easily kill more than 20 people. The substance that makes them toxic – tetrodotoxin – tastes sweet to them.


Olive Danio

Olive Danio

Olive Danio, also known as Danio dangila, is a south Asian native species. Naturally omnivorous, this fish especially likes to eat apples and bananas.

They’re quite small, never growing past 15 cm with a similarly shorter lifespan of 3.5-5 years.

Danios can survive without food for up to 14 days comfortably. Regardless of this impressive ability, they’re prone to quite easy deaths. This species spends much of its lifetime courting females and fighting rival males.

Though these fish are generally peaceful and social, losing males are often harassed to the point of death. Danio males are notorious for sneaking up on breeding grounds and eating eggs.

Danios, unlike other fish, scatter their eggs all over once laid.


Orange finned Danio

Orange finned Danio

Another peaceful Danio species, this fish, can be sometimes aggressive. A rather funny observation, they are seen to sometimes bite the tails of slow-moving long-finned fish species just out of irritation.

Because they’re naturally a freshwater species, the Orange finned danios can die if they’re not kept in a tank with a constant water current. They like to swim against a gentle flow of water.

Smallest among the Danios, this species can grow just up to is 2 inches.

The orange-finned danio is constantly moving around and rarely stops swimming, with the exception of nap time.


Ornate Tetra

Ornate Tetra

Ornate Tetras are a species of fish that can be found in small tributaries of the Amazon River.

These are sensitive to loud noises and easily startled by fast, excessive movement in their vision.

Although peaceful by nature, this fish can turn equally violent if kept with rowdy neighbors, probably something to do with their close association with piranhas and pacus.

Regardless, ornate tetras are very aquarium friendly and easy to maintain.

There’s a whole festival dedicated to the Tetra fish species in Barcelos, Brazil!

Tetras have a tendency to always munch on a thing or other, so they keep feeding on small amounts of shrimp, worms, or plankton throughout the day in the wild.

Since this fish is overly social and communal, they need at least 6-10 tankmates. Extremely communal fish species are very likely to experience depression and die; the same is the case with the Ornate tetra.




Largely known as snake mackerel, Oilfish can grow about 5 feet.

True to its name, the fish’s meat contains about 25% oil. It also has about 15% of wax esters which is a lot difficult to digest. It can very well cause severe diarrhea.

People experience quite some side effects from consuming Oilfish, including vomiting, nausea, headaches, and abdominal cramps.

Naturally, Oilfish is a solitary hunter fish that feeds on small and medium-sized fish and sea creatures. They have not been seen traveling in schools but rather alone or in pairs.

The importing of Oilfish is banned in Japan and Italy due to its severe side-effects, but mainly because many sellers were duping customers by selling them as butterfish and codfish.




A mixture between eel and snake, Oarfish is the world’s largest bony fish. An adult oarfish can weigh up to 600 pounds!

This fish is a rare sight as it lives in the deep end of the ocean. Because their natural habitat is in the depths of the ocean, they can die of exhaustion when pushed upwards by a strong current.

They have a very gelatinous gooey texture when consumed.

Studies have somewhat confirmed the Japanese folklore that describes Oarfish’s ability to sense and predict earthquakes. They are also known as messengers from the Sea God’s palace in Japanese mythology.

Even though they measure almost three times larger than humans, Oarfish aren’t at all hostile nor dangerous to humans; they don’t even have teeth.

Because of its deep natural habitat, we don’t know much about the Oarfish other than its physical attribute. This is why there’s an abundance of myths and mythological stories surrounding them.


Olive Flounder

The Olive Flounder is one-of-a-kind fish that is a highly uncommon oceanic fish.

A very distinct feature that sets this fish apart from others is its eyes. Like normal fish, baby Olive Flounders are born with two eyes on either side of the head. However, their right eye starts moving to the left side of the head as they grow. A grown adult Olive Flounder has both its eyes on one side of its head, with only one fully functioning.

The largest Olive Flounder caught weighed 22.7 pounds back in 1975 by a ship captain. An aggressive ambush predator, Olive Flounders, camouflage themselves by changing colors and sneak up on their prey as they get close.

Olive flounders have unusually large mouths. They usually stay close to the ocean floor, and when threatened, will bury themselves in the sand on the ocean floor.



Old wife

A very recognizable fish, the oldwife fish stands out because of its striped body and two dorsal fins, out of which one stands upright like a sickle.

Oldwife got its name because of the teeth grinding sound it made after being caught – supposedly sounding like an old wife. It is the only species in the Enoplosidea family.

They are endemic to Australia and are hardly found outside its vicinity. Though pretty, these fish can be fatal when touched. Their dorsal fin spines are venomous and can cause severe pain, sometimes to the point of death.



Orca killer whale

Orca killer whale

Orcas aren’t actually whales, but dolphins! The reason they share a lot of characteristics with whales is that they’ve evolved over the years. They’re also the largest member of the dolphin family.

Orcas got their name as killer whales back in ancient times when sailors saw them attacking and preying on larger whales. Initially called ‘whale killer,’ the name was eventually flipped to ‘killer whale,’ which is primarily why most people believe them to be whales.

Orcas are picky eaters. They hardly switch their diets and eating habits once they learn what their family eats. Orcas are found in every ocean in the world.

These animals are very intelligent. They can communicate with each other to pass down hunting tactics, information on what to eat, where to find it, what to avoid, etc. Each clan/pod has different accents and calls.

Orcas and humans are the only two species in the animal kingdom to go through menopause!




They’re the only species of the ape family in the world that are completely tree-living mammals. Their name literally translates to “person of the forest.”

They’re also the most patient among all apes, taking time to observe, imitate, and learn human behavior. There have been instances where they have escaped after observing their keepers.

Since they have unusually long arms, they stretch out longer than their bodies.

We share 97% of our DNA with orangutans! And guess what? Like humans, male orangutans have beards and mustaches. Their alert call sounds extremely similar to humans kissing.

The Bornean orangutan and Sumatran orangutan are critically endangered and are estimated to go extinct in the next 10 years. Sadly, they are largely consumed in Indonesia, nearing them towards extinction day by day.




Oribi antelopes are native to South Africa, graceful, and have comical, Disney-like eyes.

Only male Oribis have horns, while females have more prominent, elongated ears. In comparison, males are also much more territorial.

Oribis usually move around in a group of 4 at most.

Although they’re primarily monogamous, there have been some instances observed of polygamous variations. Oribis become sexually mature as early as 10 months!

They are also exceptional runners and will run in a zig-zag manner when trying to outrun a predator. Their top speed is around 55 kph.

They whistle as an alarm call and either hide or stand very still when they sense danger.

They are basically dwarf antelopes – the smallest of the species. Standing at 46cm, they merely weigh 2 kg at birth and 15-20 kgs as fully grown adults.

They like mornings as they are up and running right at dawn.




You might think opossums and possums are the same animals, but they’re not.

The primary difference is that while possums are found in Australia, Opossums are native to south and north America. Another point of difference is that possums are a lot closer to kangaroos, even though both, possums and opossums are marsupials.

Opossums are nocturnal and only get out during the day when they are starving.

Regardless of their looks, they are not all aggressive. If you ever encounter one and it starts hissing at you, don’t worry, it’s only a defensive bluff to look dangerous.

In reality, they’re quite scared of human interaction. And if you still continue to approach them, they will play dead out of panic. This dead-playing thing comes rather involuntary to them. The only time opossums pose a threat is their ability to easily carry and transfer diseases.

An interesting feature of Opossums is that they have a sharp memory. They’re also immune to the venom of most snakes.

Another fun fact: baby opossums are as tiny as honeybees at the time of birth.




Oryxes are desert antelopes with beautiful ringed, straight horns that are about 30 inches long. These horns are very powerful and can prove to be lethal. An angry Oryx can kill a grown lion with its horns alone.

They are also extremely fast, running up to 100 kph!

They mostly eat thorny shrubs and always feed when the temperature is low and cool, which is usually at night. Oryxes can go a couple weeks without water.

The Oryx actually went extinct in the wild back in 1972 but now has been revived. To endure the hot desert weather, Oryxes dig ditches into the sand to lie in or spend most of the day in shades resting.

Though Oryxes aren’t highly territorial, they will mark their territory with their poop. They only fight to establish hierarchy and hardly do it again after.




Oxen are primarily domestic animals used largely in agricultural practices. They are insanely strong with the ability to pull 900 or so kilograms at a steady pace.

Contrary to popular belief, oxen are actually quite smart, too – just as much as dogs. They can remember faces and places and also read body language signals.

One reason why farmers love oxen is that they do heavy work all day and only need four hours of sleep to energize back up!

Oxen are peaceful animals, mainly as a result of being domesticated for centuries. It can be an awkward sight, but oxen can be ridden just as horses; they are very obedient, calm, and patient. Muskoxen, on the other, can prove to be aggressive if threatened, especially to dogs. This species is found deeper in the north.

They are also known to swim aptly to avoid predators like wolves. Their biggest predators are polar bears and arctic wolves. When faced by predators, they will form a circle with their horns facing outwards – a tactic to scare them off and maximize damage.




At first, glance, what might somewhat look like a cross between zebra and donkey, the Okapi is the only living relative of giraffes. Incidentally, they are also a threatened species.

The only common ancestor Okapi and giraffes share – Canthumeryx – existed some 16 million years ago. The animal was first heard of in the late 1880s, with people describing it as a striped donkey. They are a relatively newly discovered species which wasn’t until the 1900s.

Just like giraffes, Okapi has super long tongues measuring somewhere between 12-15 inches. It can easily reach their ears and eyes.

Funnily enough, okapi babies are called calves, and they can walk within half an hour after their birth. These animals are territorial and like to be by themselves.

They use their feet to mark their territories which secrete a tar-like sticky marking and peeing all over.

They also have oily fur to protect themselves against rain.





Ostriches are famously known for being the biggest birds on the planet.

They also have the largest eyes of any land animal, which is 5 cm in diameter. This allows them to see as far as 3.5 kilometers! On the other hand, their brains are as big as almonds, smaller than even their eyes.

Another largest award Ostriches have is for having the largest bird eggs on earth.

Ostriches have beautiful long lashes as protection against sand and wind. They are so fast that they can cover up to 5 meters with their long legs when running.

When highly worked up, an ostrich’s kick can kill larger predators like lions, even humans. They have three stomachs but no teeth. They can also survive weeks without water.

And no, they don’t really bury their heads in the ground; it’s just a misconception.




These majestic-looking creatures are birds of prey.

Owls possess exceptional eye-sights as a result of being nocturnal. But regardless, they mostly rely on sounds to hunt at night as they also have a super-heightened hearing ability.

Owls can sometimes eat other owls, usually smaller than their size.

Most of the known information about owls is true. They can turn their heads 270 degrees; however, the blood circulation to their heads is cut off when they do this. They also have a very quiet flight.

Owls are naturally very quiet animals, so they absolutely hate sudden, loud sounds. So, if you’re worried about running into one, just clap, yell and make your presence known; they’ll stay far away.

Owls often get a bad reputation for being evil omens; they’re actually quite sweet and friendly once you make acquaintances.

One of the most distinctive features of owls is their large eyes. You’d be surprised to know that their eyes are not round but actually tubes!

The smallest owl in the world weighs about 1 and a half ounces and stands at 5 inches tall. Now, that’s tiny.




The oystercatcher is a large waddling bird. They are very easy to identify due to their long orange-red bills, black and white body, and reddish-pink legs.

They are probably the most easily recognizable among all waders in the UK. Close to being threatened, this rather large bird is found on the coasts of Europe.

The first oystercatcher species to go extinct was the Canarian Oystercatcher in the early 1900s. It’s the only seabird that is completely non-migratory.

Regardless of the name, Oystercatchers don’t actually eat oysters.

Baby Oystercatchers can very well dive and swim underwater when chased by predators. They’re quite isolated and are sensitive to human activity.

Also highly monogamous, one Oystercatcher pair was observed to be defending and settled in the same place for 20 years.

These birds are quite large, but the lightest Oystercatcher species is the Eurasian Oystercatcher, weighing just about 500-600 grams!

The longest an Oystercatcher has lived is recorded to be at 40 years, one month and two days.


Ornate hawk-eagle

Ornate hawk-eagle

The ornate hawk-eagle is a medium-to-large-sized bird of prey. Female ornate eagles are 15% larger than males and as much as 50% heavier.

These are widely spread across in abundance and commonly found in tropical forests and regions. The bird has a unique crest on the top of its head, which indicates its excitement or curiosity if raised.

A full-grown adult can range from 55 to 70 cm, with a 120-150 cm wingspan. They use a series of loud piping whistles as their call signs.

These hawk-eagles feed on small, medium, and even large-sized birds like guans. They might sometimes even prey on snakes, lizards, and small and medium-sized mammals. The ornate hawk-eagle can actually kill prey that is twice its weight.

Ornate hawk-eagles take turns grooming their chicks. Its initially the female parent that cares for the baby until it takes its first flight, after which the male parent takes over.





An Owlfly is a mix between dragonflies and butterflies with big eyes and long clubbed antennae resembling a dragonfly. Because of this unusual combination of looks, this insect is unofficially considered the ugly duckling of the insect family.

This species dates back to the mid-Mesozoic age.  Owlflies are mainly found scattered across Australia.

When touched, adult Owlflies release a slightly toxic smell as an automatic defense against predators. These are ariel predators that are seen feeding during sunsets.  Even Owlfly larvae are predators who ambush their prey by burying themselves at the top layer of the soil.

Not necessarily dangerous, but Owlfly caterpillars are feisty and will bite down on you, unlike other caterpillars.

Like most insects, Owlflies are also attracted to light.


Owl butterfly

Owl butterfly

These are fairly large butterflies mainly found in Southern and Central American rainforests. Their wingspan can measure up to 20 centimeters, which makes it very easy to spot.

Owl butterfly caterpillars are also similarly large, growing up to 15 centimeters. These are usually considered pests in plantations because of how they feed.

Owl butterflies get their name from their huge marking that resembles an owl’s eyes. This marking is quite useful as camouflage protection against predators.

These butterflies feed on fermented fruits but particularly love feeding on bananas for some reason.

Like most butterflies, Owl butterflies too have a higher chance of survival and a rather comfortable life in captivity.




There are somewhere 3000 species of orb-weaver spiders in the world.

The web of these spiders is insanely huge, measuring up to three feet in diameter! They can grow quite a lot in body size as well – up to 7-8 centimeters, including their legs. They have three claws at the end of each leg.

They aren’t aggressive at all as they don’t have enough venom to cause any real harm. But they will bite you if they are scared or threatened.

Orb weavers sometimes do not eat every prey they catch and let go of them, though they’re still pretty dead by then. Some female orb weavers eat smaller males right after mating.

Most of these spiders produce a new wen every single day.


Conclusion: Animals that Start with O

That concludes our list of animals that start with the letter O.

Surprisingly, this was the most difficult list to write yet and it certainly wasn’t because animals that start with O are obscure. It was the opposite actually. There are so many well-known animals beginning with O.

It’s been a long road, but we’ve finally made it to the end. I hope you enjoyed reading this article and were able to learn some new things along the way. Thanks so much for taking the time!

Please do share this with your friends and colleagues on social media, using the sharing buttons available on this page.

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