Monarch caterpillar season runs from late May through September across most of the United States. Southern states see them as early as March. Your exact timing depends on where you live and which generation of monarchs has made it to your area.
The answer to when do monarch caterpillars appear changes based on your spot on the map. In Texas and the Gulf states, the first monarchs fly back from Mexico in March and start laying eggs fast. Those eggs hatch into generation 1 caterpillars by late March or early April. I have friends in Houston who find caterpillars on their milkweed while I'm still waiting for the last frost up north.
Monarchs don't fly the whole trip in one go. The generation 1 butterflies head partway north and lay eggs in the central states during May and June. This second batch grows up, becomes butterflies, and flies further north to lay generation 3 eggs in late June through July. Some years bring a 4th generation in August. Then the final migratory group shows up in late summer. Each wave pushes monarchs further north. They reach Canada by midsummer.
I track my first caterpillar sighting each year in a simple log. The date moves around by as much as three weeks based on how warm the spring gets. A warm April means your milkweed sprouts sooner, which brings egg-laying females earlier. In 2023, I found my first caterpillar on June 4th. The year before, I didn't spot one until June 22nd. Your weather drives the whole schedule.
You should prep your garden well before the key monarch caterpillar months start. Cut back dead milkweed stems in early spring so fresh growth comes in strong. Make sure you have at least 10 to 15 plants to feed your caterpillars through the season. Stop all pesticide use near your milkweed by April at the latest. Spray residues can linger on your soil and leaves for weeks after you apply them.
Citizen science apps help you time your prep work well. Journey North and iNaturalist let you track monarch sightings across the country in real time. Check these apps in February to see when the first monarchs leave Mexico. Follow their path as it heads toward your state. Once you see sightings within 200 miles of your home, start checking your milkweed for eggs each morning. You'll spot your first caterpillars within days of their arrival in your area.
Read the full article: Monarch Caterpillar: Stages, Care, Facts
