Here you see a Monarch Butterfly Caterpillar feasting yesterday on butterfly weed (Asclepias tuberosa, L.), a plant in the milkweed family:
Given the date, I believe that these little fellows wearing the royal colors now are part of the last graduating class of the year. (Sex assumed.) That is, their generation will metamorphize into the Monarch butterflies that will attempt to migrate many miles to the south next month, a voyage of incredible danger for such small and fragile creatures. Their parents apparently were in one of the latter-month generations that were born here and will die here.
The migrating Monarchs (Danaus plexippus plexippus) are a subspecies of the non-migratory Monarchs (Danaus plexippus) that mostly stay in southern Mexico, Central America, northern South America, and the Caribbean.
The migratory Monarch population reportedly has shrunk at least by between 22 and 72 percent over the past decade (2021 estimates). This disaster-in-the-making has been attributed primarily to man-made causes, including milkweed habitat loss, pesticides, and harsher weather caused by climate change. (Images taken in Brooklin, Maine, on August 26, 2023.)