Assessing predation of monarch butterfly (Danaus plexippus) larvae using artificial caterpillar models

Predation of immature monarch butterflies (Danaus plexippus) by arthropod natural enemies is well-established. However, little is known about predation by avian and mammalian predators on this species. Decline of the monarch over the last several decades has led to numerous conservation programs and efforts to plant milkweed and floral resources in diverse habitats. The recent proposal to list the monarch as a threatened species may require non-lethal methods for studying predation dynamics. Here, artificial caterpillar models were used to assess predation of late instar monarchs in urban, peri-urban, and rural milkweed stands. Impressions on the larval models left behind by arthropod, avian, and mammalian natural enemies reveal higher instances of predation in rural areas. Predation by arthropods increased from May-late July and diminished in August and September. Avian predation was highest in May-early June, with an uptick in September, and rarely occurred in late July-early August. Mammalian predation was minimal. This study suggests that artificial larva can be used to study predation of a conspicuous species of conservation concern, such as the monarch, although inherent methodological limitations should be considered.