Why do monarch butterflies lay their eggs on a milkweed leaf?

Monarch Butterflies lay their eggs on milkweed leaves because this plant is the primary food source for their larvae once they hatch. Milkweed contains toxic compounds called cardenolides, which the caterpillars ingest, making them unpalatable to predators. By laying their eggs on milkweed, monarchs ensure that their caterpillars have immediate access to a suitable and protective food source as they grow. Additionally, the toxicity of milkweed helps deter potential threats, increasing the chances of survival for the young caterpillars.