Are there any pairs of animal species that regularly prey on other?
Caiman and Anacondas - though each hunts the other at a stage of development when the hunter is larger.1 2
Occasionally this occurs with Orcas and Sharks.3
Some species of shark3
Spiders and mantids4
Alligators and catfish (catfish prey on infant alligators)
Many species of predatory fish
Some species of constrictor and venomous snake.
Some frogs and Epomis circumscriptus / Epomis dejeani5
Some amphipods6
In Antiquity, hominids and lions7 8
Big cats preying on eachother, among other large predators:


Carnivores eat a variety of vertebrates: e.g. desert coyotes eat … carnivores (roadrunners, reptiles, and mammals)… Carnivorous mammals often overlap substantially in diet (30). Many “readily prey on other carnivores” (125), e.g. tigers prey on bears (black, brown, and sloth bears), dogs, wolves, lynx, and badgers (125): leopards prey on lions, cheetahs, wild dogs, and spotted hyenas (also raptors, crocodiles, and pythons; …
Leopards are mutual predators with lions, spotted hyenas, tigers, large raptorial birds, crocodiles, and pythons…

The Ecology and Evolution of Intraguild Predation: Potential Competitors That Eat Each Other