Monarch butterflies pass through on fall migration
s were observed on 2026-10-14 at The Morton Arboretum in Lisle and on 2026-10-13 in Downers Grove and Bolingbrook.1 Mid-October represents the tail end of southbound migration; monarchs breeding in the northern Great Lakes region pass through Illinois en route to overwintering sites in Mexico.1 The Monarch is a proposed threatened species under the Endangered Species Act.1, 2
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