Same Predator, Different Plant, Different Outcome

For herbivores, the effects of predators extend beyond direct predation. The risk of predation alone can change how an animal feeds, grows, and develops. For plant-feeding insects, those effects may also depend on the plant itself. In our recent study in Ecological Entomology, we asked how predation risk and milkweed species interact to shape monarch caterpillar development.

Using an outdoor common garden experiment over two growing seasons, we raised monarch caterpillars on showy milkweed (Asclepias speciosa) and narrowleaf milkweed (A. fascicularis), either exposed to naturally occurring predators or protected within predator-exclusion cages. We found that predator effects depended on milkweed identity. Caterpillars feeding on showy milkweed showed slower growth and, in one year, longer development when exposed to predators, while we detected much weaker effects on caterpillars feeding on narrowleaf milkweed.

Those differences may persist beyond the caterpillar stage. Larval growth strongly predicted adult wing area, suggesting that conditions experienced while feeding and avoiding predators can carry forward into adult morphology. Together, our results show that the effects of predators cannot always be separated from the plants on which herbivores feed.

“Food plant–associated predation risk and its impact on larval development and adult morphology in a specialist butterfly” was published in Ecological Entomology in April 2026.