There is no such thing as an herbivore: incidental and intentional ingestion profoundly affects both herbivores and plant-dwelling invertebrates.

Real-life ‘herbivores’ are not the herbivores of our simplistic ecological and behavioral models – real-life herbivores constantly consume other organisms both incidentally and intentionally, with the ‘prey’ usually consisting of plant-dwelling arthropods, smaller invertebrates, and carrion. A remarkable amount of disparate literature has amassed on these phenomena, yet the implications of these interactions are rarely considered, despite their potential importance. Here I argue that to fully understand behavior, morphology, and coloration of insect-dwelling arthropods, as well as of that of ‘large’ herbivores (whether arthropod or vertebrate), these important interactions must be considered. This perspective has two aims. The most important is to encourage researchers working on herbivores and plant-dwelling invertebrates to think more broadly about what is ingested, and what is not ingested, and why. The second is to propose several hypotheses about these interactions shape the morphology, behavior, and chemistry of these organisms. Specifically, I propose that aposematic and masquerade phenotypes, escape behaviors, feeding and pupation location, survival of gut passage, and aggregative behaviors, most of which are thought to be driven by predators, may be also driven by incidental ingestion. Lastly, to draw attention to the role that inclusion of animal food into a phytophagous diet may play in niche space, competitive interactions, and organismal nutrition. I ultimately hope this perspective encourages many creative new lines of research on the broadened phenomenon of ‘herbivory’.