The diversity of shapes, colors, sizes and behaviors that nature harbors arouses great interest and admiration for the animal and plant kingdom among the most curious. But, among all the mysteries that accompany the development of life on our planet, giant animals are one of the most shocking.
Antarctic blue whale
The blue whale or blue whale , is considered the largest animal in the world that has ever existed (there are fossil records of this species from 1.5 million years ago  ). It can measure between 24-30 m in length and weigh 130-150 tons. For you to get to imagine the size of this mammal, it is interesting to know that its tongue can weigh the same as an elephant  . Here below you will see images of comparisons of this species with other large animals.
Despite the uniqueness of this cetacean, according to the IUCN it is in danger of extinction (EN), its main threats being fishing and the degradation and alteration of its habitat as a result of climate change. We recommend you read this other article about Why the blue whale is in danger of extinction and also this other one about What is the largest whale in the world .
If we consider body length independent of weight, the boot lace worm ( Lineus longissimus ) is the longest animal in the world, ahead of the blue whale, as the name of the species indicates.
With an average length of 30 m and up to 55 m , this thin and flabby worm belonging to the edge of the nemerteans, is currently listed in the Guinness Book of Records.
Regarding its length, it is above the Antarctic blue whale and below the boot cord worm, with more than 36 m in length , but the lion’s mane jellyfish, also called the lion’s mane jellyfish, is the largest jellyfish there is.
This species of cnidarian , which inhabits the deep and cold waters of the Arctic, the Atlantic and the Pacific, owes its name to the compact appearance and the length of its tentacles, provided with stinging cells.
After the blue whale, the fin whale is the second largest cetacean in the world. With a size of up to 26 m in length and a weight of approximately 75 tons , B. physalus is characterized by its hydrodynamic and slender body constitution, which allows it to move at high speeds (more than 40 km / h)  .
This migratory mammal is one of the most social balenopeterids that exist, so its sightings and contacts with boats are very common. Currently, the conservation status of this species is vulnerable (VU) , according to the IUCN red list, its main threat being the whaling carried out until the middle of the last century.
The sperm whale ( Physeter macrocephalus ) is the largest odontocete (toothed cetacean) that exists. Being able to reach 20 m in length and up to 57 tons in weight , this peculiar species, which lives in the abyssal regions from the poles to the Equator, is easy to identify by its large and rounded head. In fact, as its scientific name suggests, it is the animal with the largest brain .
Despite being long-lived animals, the survival of sperm whales is threatened by commercial hunting and by the pollution of seas and oceans, so that their conservation status is vulnerable (VU).
The giant squid is considered the largest invertebrate on Earth , measuring 18 m in length and weighing 1 tonne . This cephalopod, like the rest of squid, has eight arms and two tentacles. It is present in all oceans and is difficult to see because it lives at great depths; Despite this, it has been identified in various places such as Norway, Newfoundland, New Zealand and Australia.
After the giant squid, the gray whale is the largest animal of this classification that we make, with a size of up to 15 m in length and 35 tons in weight. As its name suggests, this mysticete has a generally gray coloration, although it is easy to distinguish it from other cetaceans by the large number of crustaceans (specifically barnacles) attached to its skin.
Currently, the distribution of this whale is restricted to the North Pacific, although its presence was common in the waters of the North Atlantic, until it became extinct in the area throughout the 19th century due to uncontrolled commercial hunting. Despite the threats that this species has faced, its protection has been key to recovering populations and reaching a conservation status, according to the IUCN, of Least Concern (LC) .
The reticulated python is the largest snake in existence. It belongs to the Pythonidae family, of boas and anacondas, and can measure more than 10 m and exceed 100 kg in weight. This species that is distributed by Southeast Asia, Indonesia and the Philippines, lives mainly in jungles and humid forests, although it is also possible to find it in the vicinity of rivers and other bodies of water.
The whale shark ( Rhincodon typus ), more than 12 m long and weighing 34 tons , is considered the largest fish in the world . This broad, flat-headed species with eyes located on its lateral ends, is popularly known as a checkerboard, domino or lady fish, due to the gray coloration with white dots and stripes that characterizes it.
As a curious fact, this solitary animal, despite the fame that sharks have in general, is not aggressive and does not pose a danger to humans; the reality is totally the opposite, humanity being a real threat to its conservation. In this sense, the commercialization of its meat, the pollution of seas and oceans and climate change, among other factors, have led to the whale shark being in danger of extinction (EN) .
After the reticulated python, the common or green anaconda, is the second largest snake that exists, being able to measure 10 m in length and weigh more than 100 kg . Originally from South America, this grayish-olive green constrictor species lives in jungles and is commonly found in shallow bodies of water, which is why it has a great ability to swim.
The destruction of its habitat has become one of its main threats and, although its conservation status is of Least Concern (LC) according to the IUCN, this species is considered extinct in Argentina .
Killer whales ( Orcinus orca ) are among the largest animals in the world, with smaller females measuring 9.57 m and weighing up to 10.5 tons . Despite the fame that has given them the bad translation of their name in English, killer whale (who wanted to make more reference to “killer whales”, since they feed on them, and not “killer whale”), these Cetaceans are very social animals, which have always interacted with humans.
African elephants are one of the largest and heaviest land mammals in existence, standing 4m tall, up to 8m in length, and weighing more than 10 tons .
In Africa there are two types of species, Loxodonta africana and Loxodonta cyclotis , both threatened by the destruction of their habitats and by hunting specimens to trade with the ivory for their tusks. So much so that L. africana is in danger of extinction and L. cyclotis in critical danger of extinction according to the IUCN.
We encourage you to get to know them better by reading these other Green Ecology articles on Where elephants live and what they eat and Why elephants are in danger of extinction .
The giraffe is the tallest animal in the world. This African mammal that lives in savannas stands out for its long neck, which reaches 1.2 m, and for its blue tongue of half a meter in length, being able to measure a specimen in its entirety 6 m in height. Such is the size of these ruminants that, with one year of life, they already reach 2 m in height.
Currently their populations are in regression and their conservation status is vulnerable (VU) , mainly due to hunting and the destruction of their habitat due to deforestation and armed conflicts. Here you can read about Why the giraffe is in danger of extinction .
The king or Burmese cobra is one of the largest land animals in the world, reaching body lengths of up to 5.5 m and weighing up to 12 kg . This species is widely distributed in Asia (southern China, the Philippines, Indonesia, Malaysia and Myanmar, among other regions) and is one of the five most poisonous snakes that exist.
Currently its conservation status is vulnerable (VU) , deforestation being one of its great threats.
The marine crocodile, also known as saltwater crocodile, estuary or porous crocodile, is the largest reptile on the planet, reaching 4.5 m and weighing 2 tons . This primitive-looking species inhabits estuaries, swamps, lakes, and coastal areas of India and Australia.
After the marine crocodile, in this classification of the largest animals in the world, we find the Nile crocodile, with an average size of 4.2 m (although there are specimens that reach 5 m ) and up to 730 kg of weight.
This species, despite reaching its near extinction between the 40s and 60s of the last century due to the indiscriminate hunting of its specimens, its populations are stable and currently presents a conservation status of Least Concern (LC) .
The hippopotamus is another of the largest land animals on our planet. With an average body length of 4 m and a weight that ranges between 3,000 and 4,500 kg , this African mammal owes its name to its amphibian lifestyle. In fact, shallow bodies of water, such as rivers, lakes, lagoons, spend most of the time.
Currently threatened by hunting and habitat destruction, the hippo’s conservation status is Vulnerable (VU) .
The polar bear, also known as the white bear, is a large animal, which can measure between 2.3 m and weigh up to 700 kg . In fact, arctic pups weigh about 600 g at birth and reach 15 kg in their first months of life.
According to the IUCN, the conservation status of the polar bear is vulnerable (VU) , but its decline is progressing very fast since it is one of the species most threatened by the melting of the polar ice caps. Read this other article to learn more about this species: Is the polar bear in danger of extinction?
Finishing this list we find the ostrich ( Struthio camelus ). Considered the largest bird in the world, adult individuals of this flightless species can reach 2.4 m in height and weigh about 140 kg . In fact, such are the dimensions of this species of flightless bird that the eggs can weigh on average 1 kg.
Another reptile that deserves a place on this list is the famous leatherback turtle, the largest species of tortoise in the world . It is a sea turtle that is also called the giant sea turtle or leatherback turtle and is considered the largest in size with quite a difference from the other species, since it can weigh more than 600 kg and can reach up to 2.5 meters in length. .
According to the IUCN Red List of Threatened Species, it is in a state of vulnerable (VU) to extinction. Here you can read more about the question: Is the leatherback turtle in danger of extinction?
The Goliath tarantula, also called the giant or aviary tarantula is considered the largest arachnid that exists. This arthropod, which can measure 30 cm -equivalent to the height of an A4-size paper- is capable, due to its large size, of feeding on small insects, lizards, rodents and even some birds, for which it receives the name of aviary tarantula. Although it may not seem like a very large animal at first glance and comparing it with others on this list it is small, taking into account that it is a spider, we can say that it is huge.