There’s a bug in my salad: assessing the ingestion of insects by ungulates using DNA metabarcoding

Large mammalian herbivores (ungulates) greatly influence insect herbivores (IH) both directly and indirectly. The indirect effects, that are mediated by changes in plant traits, have been thoroughly studied. However, direct effects, such as ingestion of IH by ungulates, have been overlooked. It is not yet clear whether or how ungulates react to the presence of IH (especially noxious or unpalatable species) on their food plants. Here, we show that ungulates are capable of detecting IH on plants and possess highly efficient behavioral mechanisms that allow them to avoid IH ingestion while feeding. While noxious or unpalatable IH are avoided, harmless or small insects may be readily ingested by ungulates. To assess the ingestion of IH by grazing ungulates at the community level, we performed DNA metabarcoding on feces of free-ranging ungulates (goats) using primers targeting mitochondrial markers (COI) of arthropods. We found that goats indeed ingested a variety of arthropods (including beetles, butterflies and spiders). Highly mobile arthropods that can escape the risk of being ingested (e.g. bees and grasshoppers) were rarely consumed. This study provides new ecological perspectives on the importance and ubiquity of direct interactions between mammalian and insect herbivores in terrestrial trophic cascades.