Data story 06 ยท Seasons
No milkweed, no monarchs
Monarch caterpillars eat only milkweed. In Ontario, milkweed comes up in May, the first monarchs arrive around the same time, and eggs appear about two weeks later. Here is the whole season, week by week.
Read it right
Every chart has limits. Here is what this one can tell you, and what it cannot.
What this shows
- The Ontario season, week by weekWhen people reported common milkweed, monarch eggs and caterpillars, and adult monarchs, from 2016 to 2025.
- Eggs follow the milkweedMonarch eggs show up about two weeks after the milkweed does.
What it does not show
- AmountsHow much milkweed, or how many monarchs, there are.
- An even picture of the seasonThe spike at the end of July is the Monarch Blitz, when thousands of volunteers look at the same time.
Sources. GBIF.org occurrence records for Ontario (GADM CAN.9_1), 2016 to 2025: Asclepias syriaca and Danaus plexippus with a recorded life stage (CC0, CC BY and CC BY-NC). The narrated tour is read by an AI voice (OpenAI gpt-audio, via OpenRouter) from the captions you see. See Data and credits. No endorsement implied.