Monarchs have four life stages, and the timing is fairly predictable, though it shifts with temperature. Here is information to help with planning to have enough milkweed.
1. Egg (3–5 days)
Females lay single eggs on the underside of milkweed leaves. This is fast — no feeding needed here, just make sure you have milkweed available for egg-laying.
2. Larva / Caterpillar (10–14 days)
This is the stage that matters most for your planning. The caterpillar goes through five instars (growth phases between molts), and it eats milkweed almost exclusively — nothing else will do, since milkweed’s toxins are what make monarchs unpalatable to predators later in life. Eating ramps up dramatically as they grow:
- Instars 1–2 (first ~4 days): tiny, eat very little
- Instars 3–4 (next ~4 days): appetite increases noticeably
- Instar 5 (final ~4–5 days): this is when they do the vast majority of their eating — a single 5th-instar caterpillar can strip a milkweed plant almost bare in a day or two
3. Pupa / Chrysalis (8–12 days)
No eating at all here. The caterpillar forms a chrysalis (often on a sturdy stem, fence, or nearby structure, not necessarily the milkweed itself) and undergoes metamorphosis.
4. Adult butterfly
Emerges and lives anywhere from 2–6 weeks (summer generations) up to 8–9 months (the migratory generation that overwinters in Mexico).
Planning tip for plant quantity: the rule of thumb many monarch gardeners use is 4–6 mature milkweed plants per caterpillar to get it safely through instar 5, since that final stage consumes so much foliage so quickly. If you’re hoping to support multiple caterpillars at once (which is common if several eggs get laid around the same time), plant generously and consider succession planting or having a few plants in reserve, since a hungry 5th instar can defoliate a plant faster than it regrows.
Note: milkweed is the only genus (Asclepias) monarch caterpillars will eat — common milkweed, swamp milkweed, and butterfly weed are all good options depending on your soil and sun conditions.
