Many of the largest animals on Earth live in the ocean, making accurate identification rather difficult. Some of them, such as the Colossal Squid, have never even been seen in adult form, leading to debate over how large they actually get. Fortunately, a large assortment of land animals are also quite large, and they are much easier to measure. However, it is important to remember that the largest animals on Earth are eclipsed in size by some organisms, such as the honey fungus, which can cover areas of ground measured in miles with its mycelium, and the General Sherman Tree, a giant sequoia in California, which is estimated to weigh almost 10 times more than a blue whale.
The generally accepted largest animal on Earth in terms of size and volume is the blue whale. The largest blue whale ever weighed was a 210 ton female. Blue whales roam the oceans of the world, and are considered to be seriously endangered, despite efforts on the part of biologists to save them. The exact number of blue whales on Earth is unknown, but is estimated between five and 12 thousand individuals. Blue whales may be among the largest animals on Earth to exist ever, as they are larger than any of the dinosaurs were.
Among the largest animals on Earth are a number of sea going creatures such as the Lions Mane Jelly, which can actually grow to be longer than a Blue Whale. The Man O'War can also get extremely long, but since it is a collection of organisms rather than an individual, it is usually not counted in the list of the largest animals on Earth. The Japanese Spider Crab is also quite large. Given the large portions of the ocean which remain unexplored, it is possible that there are more large organisms lurking in the depths of the ocean.
The ocean isn't the only place to find big creatures. On land, many of the largest animals on Earth can be found in Africa. Bush elephants are the largest land going mammal, and hippopotami are close behind. Saltwater crocodiles are the largest reptiles on Earth, and the Chinese Giant Salamander has the title of largest amphibian. Birds are represented by the ostrich, and the Goliath beetle is the largest insect.
As can be seen, several of the animals considered to be the largest animals on Earth are also under threat. Many large animals take some time to mature, making them vulnerable to predators when they are young. Many large animals also unfortunately have body parts which are valuable to humans, such as ivory. Many of the largest animals on Earth were indiscriminately hunted by humans, resulting in serious problems for their populations, which also reproduce more slowly than small animals.