The butterfly's life cycle requires food for both the adult and caterpillar stages. Certain butterfly species will lay eggs on only one, or a few, plant species. Other butterflies lay eggs on many plant species. Generally, butterflies lay eggs only on plants that are appropriate as a larval food source, although this is not always the case. Tiger swallowtails feed on tulip poplar, and the mourning cloak on aspens.
Monarch caterpillars feed on milkweed leaves.
Milkweed contains toxins that the larvae can ingest without harm, but which makes the caterpillars unpalatable to predators. Butterflies may lay their eggs on or near the kind of plants on which the caterpillars feed. The caterpillar may prefer the leafy parts of a variety of host plants, including flowers, vines, shrubs, trees, and weeds. Unlike caterpillars, adult butterflies feed on a variety of nectar-producing flowers. You can observe them through late fall.