Being giant doesn't necessarily mean being easy to see.
Some of nature's largest animals behave shyly or know how to camouflage very well, remaining mysterious to scientists.
Check out ten of them that are rarely seen:
Large armadillo (Priodontes maximus)
In theory, it seems easy to spot something the size of a pig, covered with scales and with claws up to eight inches like a small sword. But the giant armadillo is great at hiding, so scientists had to install secret cameras to understand more about the animal.
"Very few people have ever seen a giant armadillo in the wild," says biologist Arnaud Desbiez, coordinator of the Tatu-Canastra Project in the Pantanal. "Even the owner of the farm where our base, which was born and raised here, had not seen one of these animals before we started the project."
Weighing up to 50 pounds and reaching a maximum of 1.5 meters in length, it is the largest armadillo species on the planet - measuring almost twice its "cousins" in the same family.
Size, however, does not help you curl into a ball to protect yourself, as other armadillos do. Instead, he digs underground burrows with his claws and only ventures out into the darkness.
The giant armadillo is considered a vulnerable species because of hunting and destruction of its habitat.
Giant squid (Architeuthis)
The giant squid is probably the most abominable of all giant animals. Its name is due to its body being 5 meters long, and its pair of tentacles extending - making its final size reach 13 meters.
The predator is known to have football-sized eyes and a giant mouth that can destroy its prey in seconds.
But as the animal lives deep within the ocean, up to 1,000 meters below the surface, few people have ever had a chance to see one alive.
There are many legends and stories of these creatures attacking ships, but documented records of such encounters are rare. Most often, they occur on the surface when the squid is injured or dying.
The first time a giant squid was filmed in its habitat was in 2012, during a project organized by a team of scientists of various nationalities that launched a submersible vehicle off the coast of Japan.
Giant otter (Pteronura brasiliensis)
Although there are no elephants, the tropical strip of South America is still a land of giants. The continent is home to the largest members of the armadillos and anteaters families, as well as the capybara, the largest rodent in the world.
The giant otter, which lives in the rivers east of the Andes, is twice the size of the largest species in the family, and can reach 2 meters in length.
The animal lives in open habitats in large family groups and can easily be spotted. But while it can cope with its natural predators, such as the alligator and the jaguar, the giant otter turned out to be a big victim of hunting, probably because of its docile and curious personality.
Its leather was once quite valuable and its trade was banned in 1975. Today, however, the giant otter is threatened by human activity in the Amazon and the Pantanal.
Giant Huntsman Spider (Heteropoda maxima)
If the size of a spider is measured by the length of its legs, the largest one reaches 30 centimeters and goes by the worrying name of "giant hunter spider". Fortunately, its predatory activities are limited to insects.
It's very possible that you'll never see one of them crossing the floor of your house unless you live in a cave in Laos. But even there, it's hard to spot her.
This species made news among spider enthusiasts and haters around the world when it was discovered in 2001 by biologist Peter Jaegar of the University of Mainz in Germany.
He said the hype was not good for the species because of the demand for exotic, often illegal pets. The biologist believes that for every 100 spiders that reach their final destination, another 1,000 die when they are removed from their habitat.
Jaegar hopes this spider's short life will eventually diminish interest in her.
Rowfish (Regalecus glesne)
With the appearance of a giant sea serpent, the paddle fish is extremely flat and moves across the rippling waters.
Its long pelvic fins look like oars, and its head has an unusual red crest. But its most striking feature is its size: up to 17 meters in length, making it the largest bone fish in the world.
Despite being huge, the paddlefish is one of the most mysterious creatures on the planet. He lives in the depths of the ocean, along with other giants. It is not yet known why species in this habitat are so large, but there are hypotheses about the influence of low temperatures, high pressure, lack of sea currents and food shortages.
Because of their deep sea habits, it is rare to spot a paddle fish. In recent years, unmanned submarines have managed to film the animal in its natural habitat.
The fish only comes to the surface when it is injured or dead. In June 2015, a 5.2-meter specimen appeared on a beach on Catalina Island, California - the third to emerge there.
The largest frog in the world can weigh 3.2 pounds - the equivalent of many newborn babies. This frog may be gigantic, but like many of its amphibious cousins, it is a master of camouflage. Its greenish color helps it hide among mossy rocks.
The animal lives near fast-flowing rivers in the coastal forests of West Africa. Contrary to popular belief, the frog does not have a vocal pouch. Therefore it cannot make noises like its relatives, needing to whistle to attract a partner.
But despite its tricks, this anuran is an endangered species: its population has fallen 50% over the last three generations. This is because it is much appreciated as food and is also popular among exotic pet breeders.
Captive breeding programs have not been successful, leading environmentalists to try to work closely with African communities to avoid unsustainable hunting.
While most insects fit in the palm of any adult, this class of animals also has their giants. The largest of these is a stickman living in Borneo, discovered in 2008.
The largest known specimen measures 50 centimeters with legs straight and is now part of the London Natural History Museum's collection.
Scientists know very little about this insect because it is exceptionally difficult to find in nature. Males are brown and females greenish. Both are long and thin, and prefer to live in the treetops, which facilitates their camouflage in the rainforest.
As masters of disguise, the stickworm's female lays eggs that look like seeds and have wing-shaped extensions, which help them spread in the wind.Continues after advertising
In Papua New Guinea lives a butterfly so large that it is mistaken for a bird.
THE Ornithoptera alexandrae It focuses on a small area of rainforest near the coast. The male is spectacular, with iridescent blue-green stripes on its velvety black wings, and a vibrant yellow abdomen. The female is a bit more discreet, with more beige tones. They, however, are 30% larger, reaching a record 30 cm wingspan.
The insect was discovered in 1906 and soon after became one of the most coveted by collectors. So it was overhunted.
Even banned in 1966, poaching and habitat destruction dramatically reduced the population of these butterflies. Local tribes and environmentalists are working to save them.
Giant isopod (Bathynomus giganteus)
Imagine a cat-sized little cat - 76 centimeters long and weighing 1.7 pounds. Well, this creature exists and is called the giant isopod.
It is a crustacean, a distant relative of shrimp and crab, which lives well below the sea surface.
The animal has the same rigid exoskeleton as its terrestrial cousins, and is able to curl up like a ball to protect itself. Lilac in color, it has seven pairs of paws, two pairs of antennae and huge eyes.
In the cold waters of the American coast, this isopod lives on the seabed 2,000 meters deep and feeds on the bodies of whales, fish and squid.
As the animal attacks fishing nets, they are often spotted when they are dragged along with fish.
Because of this, it is a species easily found in aquariums around the world, especially in Japan, where they are particularly popular.
The scientific community has not yet agreed on which species of owl is the largest in the world, but the Bubo blakistoni She is a favorite - she weighs 4.6 pounds and has a wingspan of almost 2 meters.
The species was discovered by naturalist Thomas Blakiston in 1883. It lives in forests near rivers in Siberia, northeast China, North Korea, and Japan, and feeds primarily on fish.
Finding it today is a rare fact. Because of the persecution of hunters, the reduction of fishing reserves and the destruction of their habitat, this owl is considered an endangered species.
On Hokkaido Island in Japan, this animal was considered a spirit that protected the villages of the Ainu indigenous people. Today, locals are struggling to save the species by building artificial houses.