By asking who, I assume you mean human groups. Thus, I would answer people or industrialists who pollute the air and water. And another fierce enemy would be poachers. These hunters do not obey the hunting laws that are designed to preserve the species.
the mycenaean and the dorians
All animals are territorial creatures. Hamsters are more aggressive animals when dealing with the same gender. If you have two male or female hamsters in one cage, you are begging for trouble.
There are many animals that are worst enemies but one of them are the human being an tigers. This pair of animals are worst enemies because poachers kill tigers for their fur and sometimes poachers are killed by tigers.
Whatever goes upon two legs is an enemy.Whatever goes upon four legs, or has wings, is a friend.No animal shall wear clothes.No animal shall sleep in a bed.No animal shall drink alcohol.No animal shall kill any other animal.All animals are equal .
When David was a shepherd boy he killed a lion and a bear as well.
There are two different ways that animals can protect them selves there's camouflage, weapons (animal parts used for attack)
Giant squids only have one main natural enemy - the sperm whale, which preys upon them. There has been evidence from the bodies of sperm whales that these two ocean dwellers engage in fierce battles far beneath the water's surface. Smaller squid are eaten by lots of other animals including albatross and humans.
"I will work harder" and "Napoleon is always right"
Enemies are never formed for life. Two enemies can be turned to friends easily.
Anyone invloved in a peace ceremony are former adversaries. Meaning they are all enemies.
Flash's arch enemies is the two zooms
Almost two-thirds of all named species of animals on Earth are arthropods. Arthropods are animals like crustaceans, spiders, and insects.