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How to identify it
- Wings are rusty or tawny orange above with black veins and black edges dotted with small white spots, and lighter orange or yellow-brown underneath; the wingspan is 3 1/2 to 4 inches.[1]
- Females have darker veins; males have a black spot on each hind wing.[1]
- Caterpillars grow to about 2 inches. They are banded white, black and yellow, with a pair of long black filaments near the head and a shorter pair near the rear end, and are usually found on milkweed.[1][8]
- The chrysalis is green with gold tinges, and the caterpillar hangs in a J shape before forming it.[10]
Where it lives
Native to North and South America, it has spread to Australia, New Zealand, Pacific islands and parts of the Iberian Peninsula. In North America the Rocky Mountains roughly divide the eastern migratory population, which overwinters in central Mexico, from the western one, which overwinters along the California coast; some monarchs stay year-round in parts of Florida, the Gulf Coast and California.[2][9]
Biology and life cycle
A female lays 100 to 300 eggs over her life, and the eggs hatch in about four days.[8][1]
Caterpillars feed on milkweed for about two weeks before forming a chrysalis, and the butterfly comes out roughly two weeks later.[1][10]
Summer adults live 2 to 5 weeks, and there are up to four generations each summer, each moving a little farther north.[8]
The last generation of the year doesn't breed. It flies south to overwinter, can live as long as nine months, and starts laying eggs on milkweed as it moves north again in February and March.[8][1]
Eastern monarchs may fly more than 2,000 miles to Mexico, where they cluster in oyamel fir forests from October to late March; western monarchs migrate about 300 to 1,000 miles to the California coast.[2][9]
Damage and signs
- No damage to gardens or crops: caterpillars eat only milkweeds, and adults drink nectar from many flowers, particularly New England aster and other members of the sunflower family.[1]
- Monarch numbers are falling. USFWS lists loss and degradation of breeding, migratory and overwintering habitat, insecticide exposure and climate change as threats; MDC adds herbicides that remove milkweed.[3][1]
Health risk
No risk to people is described. Caterpillars store toxic compounds (cardenolides, or cardiac glycosides) from milkweed, and their bright colors warn birds and other predators that they are toxic.[2][1]
Control
Prevention
Plant native milkweeds for the caterpillars and native wildflowers that bloom through the whole season for the adults. USFWS says even a balcony or a small yard can help, and suggests seeds and plants sourced locally.[1][5]
Skip tropical milkweed (Asclepias curassavica). Its long blooming period helps spread the parasite Ophryocystis elektroscirrha (OE) between monarchs; USFWS suggests replacing it with native swamp, butterfly, common, whorled or showy milkweed, depending on your area.[5]
Think twice about raising caterpillars indoors. Penn State Extension notes that captive rearing helps disease spread and that reared monarchs may be less likely to survive migration; it cites a Xerces Society suggestion of no more than ten per person per season, collected locally and released where they were found.[10]
Federal threatened-species proposal
In December 2024 the U.S. Fish and Wildlife Service proposed listing the monarch as a threatened species under the Endangered Species Act, with species-specific rules under section 4(d) and about 4,395 acres of proposed critical habitat at overwintering sites in seven coastal California counties.[3][6]
The comment period was reopened in March 2025 and ran until May 19, 2025. The listing takes effect only if a final rule is published; the USFWS monarch page still presents it as a proposal, so check that page for the current status.[7][6][2]
The proposed 4(d) rule would exempt incidental harm ('take') from planting, maintaining or removing milkweed and nectar plants on residential properties, or collecting, rearing and releasing 250 or fewer monarchs a year. Whether to exempt pesticide use was left open for public comment.[4]
Critical habitat places no requirements on state or private land unless a project involves federal funding, permits or approvals.[3]
Missouri's Department of Conservation notes that in July 2022 the International Union for Conservation of Nature placed the migratory monarch on its Red List as endangered. The IUCN is an international organization, and its Red List is separate from the U.S. listing process.[1][2]
Where sources disagree
How far they fly: USFWS says eastern monarchs may fly more than 2,000 miles to Mexico; the Forest Service says 2,000 to 3,000 miles.[2][8][9]
How much they have declined: USFWS puts the eastern migratory population down about 80% and the western one down more than 95% since the 1980s; the IUCN figures quoted by MDC are 84% for the eastern population (1996 to 2014) and an estimated 99.9% for the western one (1980s to 2021).[3][1]
Time in the chrysalis: MDC and Penn State say about two weeks; the Forest Service says as few as five days.[1][10][8]
Common questions
- Will monarch caterpillars hurt my garden?
- No. They eat only milkweed.[1][8]
- How can I help monarchs?
- Plant native milkweeds and a variety of native nectar flowers, and avoid tropical milkweed.[1][5]
- Is the monarch butterfly endangered?
- USFWS proposed it as a threatened species in December 2024. The listing applies only once a final rule is published, and the USFWS monarch page still describes it as a proposal. Separately, the IUCN, an international organization, placed the migratory monarch on its Red List as endangered in 2022.[3][6][2][1]
Sources
- Missouri Department of Conservation, “Monarch (Field Guide).” mdc.mo.gov/discover-nature/field-guide/monarch (accessed 2026-11-11)
- U.S. Fish and Wildlife Service, “Monarch (Danaus plexippus) species profile.” www.fws.gov/species/monarch-danaus-plexippus (accessed 2026-11-11)
- U.S. Fish and Wildlife Service, “Fish and Wildlife Service Proposes Endangered Species Act Protection for Monarch Butterfly (press release, December 10, 2024).” www.fws.gov/press-release/2024-12/endangered-species-act-protection-monarch-butterfly (accessed 2026-11-11)
- U.S. Fish and Wildlife Service, “Questions and answers: Monarch 4(d) rule.” www.fws.gov/question-answer/questions-and-answers-monarch-4d-rule (accessed 2026-11-11)
- U.S. Fish and Wildlife Service, “You can help save the monarch.” www.fws.gov/initiative/pollinators/monarchs/help (accessed 2026-11-11)
- U.S. Fish and Wildlife Service, Federal Register, “Threatened Species Status With Section 4(d) Rule for Monarch Butterfly and Designation of Critical Habitat (proposed rule, 89 FR 100662, December 12, 2024).” www.federalregister.gov/documents/2024/12/12/2024-28855/endangered-and-threatened-wildlife-and-plants-threatened-species-status-with-section-4d-rule-for (accessed 2026-11-11)
- U.S. Fish and Wildlife Service, Federal Register, “Reopening Comment Periods for Three Proposed Rules (March 19, 2025).” www.federalregister.gov/documents/2025/03/19/2025-04443/endangered-and-threatened-wildlife-and-plants-reopening-comment-periods-for-three-proposed-rules (accessed 2026-11-11)
- USDA Forest Service, “Monarch Butterfly Biology.” www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/biology/index.shtml (accessed 2026-11-11)
- USDA Forest Service, “Monarch Butterfly Migration and Overwintering.” www.fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/migration/index.shtml (accessed 2026-11-11)
- Penn State Extension, “Raising Monarchs at Home: More Harm Than Good? (updated June 2024).” extension.psu.edu/raising-monarchs-at-home-more-harm-than-good (accessed 2026-11-11)
- iNaturalist, “Danaus plexippus taxon page (order and family).” www.inaturalist.org/taxa/48662 (accessed 2026-11-11)