Why are all herbivores primary consumersbut not all primary consumers are herbivores?

All herbivores are classified as primary consumers because they directly consume plants, which are the primary producers in an ecosystem. However, not all primary consumers are herbivores because some can be omnivores or detritivores that feed on a combination of plant material and other organic matter. For example, some omnivorous species may consume both plant and animal matter, allowing them to fit into the primary consumer category while still not being strictly herbivorous.