Media release

From: The Royal Society

Caterpillars of the iconic Monarch butterfly may drink toxic latex from leaf veins to use for their own defence. Monarch caterpillars are known to sever milkweed leaf veins to stop toxic latex flowing into their feeding sites. Young caterpillars, and related species, avoid latex or regurgitate it when fed, however older monarchs “eagerly drink” the toxic sap. The authors hypothesise this ‘sabotage to consume’ adaptation could be exploiting plants for defensive cardenolide compounds.

Summary: Monarch caterpillars (Danaus plexippus) have long been thought to sabotage the veins of milkweed leaves simply to avoid the plant's toxic latex while feeding. However, recent research has revealed a more complex behaviour. While young caterpillars avoid latex, older caterpillars actively consume it, probably to increase their intake of cardenolides, compounds used to defend against predators. This contrasts with the consistent latex avoidance of non-sequestering caterpillars of the common crow butterfly (Euploea core). The Monarch's strategy evolves from avoidance in the early stages to deliberate consumption later, a remarkable adaptation to enhance its defences through increased cardenolide sequestration.