Endangered species. While protection for endangered wolves is still in question, a rare aquatic insect was denied endangered species protection this month. Its declining population is said to be related to fast-disappearing glaciers at a national park. On this Earth Day, we take a look at some animal species that have long been on the critical list.

Pacific walrus
These endangered marine mammals can weigh an astonishing amount and live in this ocean. Their numbers declined rapidly after they were heavily hunted for their blubber and ivory.
Northern flying squirrel
They are not capable of flight like birds, but the nocturnal Northern flying squirrel glides effortlessly between trees. Find out how far they can go.
Tiger
A powerful predator, the tiger's six remaining species are facing extinction, and all are under protection. Yet an illegal act still threatens their existence.
Polar bear
The world's largest land carnivore is threatened by a global phenomenon, according to scientists, that is depleting their sea ice habitat
Magellanic penguin
These adorable penguins can be found on a continent with a typically warm climate but are considered threatened due to their proximity to oil spills.
Bluefin tuna
These massive fish have become extinct in this sea as well as in the largest enclosed body of water on Earth.
Giant panda
Native to an Eastern country, the giant panda is endangered because of farming and deforestation.
Monarch butterfly
The endangered monarch uses its poisonous toxins as a defense mechanism from predators and is threatened by deforestation.
Mountain gorilla
The males of these endangered animals can grow to the size of a tall human.
Pygmy elephant
Scientists believe these small elephants separated from their larger relatives possibly 300,000 years ago. They are found on the largest island in the world.