Is it possible for a prey to become its main predator's predator?

Question

This is actually for a worldbuilding project, but I thought I'd just ask it here as it is solely about biology. Anyway, would it be possible for a herbivore, let's call him X, that is predated by a predator, or Y, to evolve to become a specialized hunter of Y? For example, wolves hunt deer. Imagine that in millions of years, the deer has evolved into the main predator of wolves. If that's not possible, is it at least possible for X to evolve adaptations for fighting/killing Y (Not for food)? If you require any further context or clarification, please let me know.

Answer 1

Interesting question! I'm going to go with a "no" for this one based on the following reasons

1. Morphology (body structures)
2. Digestive systems
3. Behavior

Herbivore and carnivore are really general categories that are reflecting distinct evolutionary paths life on Earth has taken. As such, species that we would classify as herbivore or carnivore have adapted to fit these roles nicely. Using your example, the many species of deer on Earth have classic herbivore body structures, such as eyes on the side of the head and dentition for eating plants. Carnivores have front-facing eyes and dentition for hunting and killing prey.

Prey species, specifically herbivores, have long digestive systems optimized to extract nutrients from plant material, whereas carnivores have short, efficient digestive systems.

Prey species have evolved behaviors for avoiding predators. Some remain still, some form protective circles, etc. Most of these behaviors are instinctual.

All of these characteristics will not simply disappear. Even if a prey species had a change in behavior and tried to prey upon its main predator, it would be unsuccessful due to other characteristics that just don't accommodate the organism becoming a predator.