Answer by
nrw24 (53)
As caterpillars, monarch butterflies feed on the milkweed plant, which countain poisonous compounds known as cardenolide aglycones. These compounds retain their toxicity, and persist in the insects body through metamorphosis, making the adult butterfly poisonous as well. As adults, monarch butterflies feed on the nectar from a variety of different flowering plants, much like other butterfly species.