Monarch Watch 2025: Collect your data on iNaturalis!

📝 John Lowry

The summer solstice has come and gone so we are ‘officially’ into the summer season. With the arrival of the warmer weather, it is high time to be on the lookout for that summer visitor, the beautiful Monarch butterfly (Danaus plexippus).

Monarchs have been advancing north from their overwintering sites in Mexico since the spring and by May were being reported in New York State and Michigan.

June iNaturalist records indicate that there have been early Monarch sightings in Southern Ontario – including in our South Shore region. Other sightings by mid-June include Toronto and closer to home at Presqu’ile Provincial Park and near Campbellford.

Monarch; Photo: John Lowry 

We are asking SSJI supporters to please be on the lookout for both Monarch butterflies and their caterpillars. The caterpillars are commonly found on Common Milkweed (Asclepias syriaca) but are also known to feed on other milkweed species including Swamp Milkweed (Asclepias incarnata) and Butterfly Weed (Asclepias tuberosa).

Common Milkweed

Monarch caterpillar on Swamp Milkweed; Photo: Marilyn Lauer

To collect important species specific data, sightings of Monarchs and/or their caterpillars should be recorded on iNaturalist. Observations occurring within the South Shore Key Biodiversity Area (KBA) will be automatically uploaded to our South Shore biodiversity project – entitled “Biodiversity of Prince Edward County’s ‘South Shore.’” (learn more about this project here)

Viceroy; Photo: John Lowry

On a cautionary note – please be aware that the Viceroy butterfly looks very similar to the Monarch. It is generally smaller and can be readily differentiated from Monarchs by an additional black line across the Viceroy’s hind wings.

If you have any questions, please free to reach out to John Lowry at [email protected].