Here are some possibilities:
Predator-Prey Relationship:
* Lions and zebras: Lions hunt zebras for food, while zebras try to avoid being eaten.
* Wolves and elk: Wolves prey on elk, and elk have evolved strategies to avoid wolf predation.
* Sharks and seals: Sharks are apex predators that hunt seals, which try to avoid becoming shark food.
Competition for Resources:
* Coyotes and foxes: They compete for the same prey, leading to territorial conflicts.
* Hawks and owls: They hunt similar prey, leading to occasional clashes.
* Squirrels and chipmunks: They compete for food and nesting sites, leading to skirmishes.
Natural Rivals:
* Snakes and mongooses: Mongooses are known to kill snakes, and snakes are understandably wary of them.
* Bulls and matadors: While this is a staged event, it highlights the natural aggression of bulls towards humans.
It's important to note:
* Most animals don't actively seek out conflict. They mostly interact based on instinct, survival needs, and the availability of resources.
* The relationship between two animals can be complex and vary based on the environment and circumstances.
Ultimately, the answer to your question depends on what you consider a "worst enemy." There's no single pair of animals that universally fits the bill.