The monarch caterpillar diet is milkweed and nothing else. Your caterpillars feed only on plants from the genus Asclepias. No other plant will work as a stand-in. Without milkweed in your yard, monarchs can't survive there at all.
North America has over 70 milkweed species, but not all work the same as monarch caterpillar food. Pocius et al. 2021 found that common milkweed and swamp milkweed grow the healthiest caterpillars with the best survival rates. Tropical milkweed feeds them fine but creates a problem. It stays green all winter, so OE parasites pile up on the old leaves year-round.
The amount of monarch caterpillar food that one caterpillar eats blew my mind when I first raised them. A 5th instar eats more milkweed than all four earlier stages put together. I watched one strip a full milkweed stem bare in just two days. Over its full two-week life, a single caterpillar can chew through 15 to 20 large leaves. If you have several caterpillars, your plants will thin out fast.
This milkweed-only habit exists because of a defense trick your caterpillars use. Milkweed holds cardenolides, a type of toxin that stops the hearts of most animals. As your caterpillar eats, it pulls these toxins through its gut and stores them in its body. The poison makes both your caterpillar and the adult butterfly taste awful to birds. No other plant makes the right kind of toxin for this trick to work.
Northern States
- Common milkweed (A. syriaca): Your best pick for caterpillar health and survival. It grows wild in fields and roadsides across the Northeast and upper Midwest.
- Swamp milkweed (A. incarnata): Grows well in wet soils and garden beds with regular water. You'll love the pink flower clusters that draw in adult monarchs.
- Butterfly weed (A. tuberosa): Handles dry soil and poor ground well. Your caterpillars grow a bit slower on it than on common milkweed.
Southern States
- Green antelopehorn (A. viridis): Built for Texas and Gulf heat. It handles the drought that kills most northern milkweed types in your garden.
- Aquatic milkweed (A. perennis): Perfect if you have low, wet spots in your yard where other milkweed species drown from too much water.
- Skip tropical milkweed: If you must use it, cut your plants to the ground every 3 to 4 weeks to stop OE parasite spores from piling up.
Plan to grow 5 to 8 milkweed plants per caterpillar you expect to host. If you had 10 caterpillars last year, aim for at least 50 plants this season. Stagger your planting dates or grow a few different species. This way you always have fresh milkweed for monarch caterpillars from May through September. I plant in two waves each spring so my garden never runs dry.
Cut back your milkweed for monarch caterpillars after they finish eating each stem. Your plants will send up fresh growth within 2 to 3 weeks. Water during dry spells too. Stressed milkweed pumps out extra latex sap that can trap and kill tiny first instar caterpillars before they get their first real meal.
Read the full article: Monarch Caterpillar: Stages, Care, Facts
