# Monarch Butterfly — Facts, Threats & Conservation

*Danaus plexippus (Linnaeus, 1758) — family Nymphalidae, subfamily Danainae*

> The monarch butterfly (Danaus plexippus) is an orange-and-black North American butterfly whose migratory population travels up to 4,000 km to overwinter in Mexican fir forests; the migratory subspecies is listed Vulnerable, and it breeds only on milkweed.

**IUCN status:** Migratory monarch (D. p. plexippus) assessed Vulnerable; the species as a whole is Least Concern  ·  **WARN range:** North America, Central America — Mexican overwintering forests, Introduced populations in Australia, New Zealand and Iberia

## Quick facts
| Fact | Value |
| --- | --- |
| Wingspan | 8.9–10.2 cm |
| Larval food plant | Milkweed (Asclepias spp.) only |
| Migration | Up to 4,000 km, eastern North America |
| Overwintering | Oyamel fir forest, central Mexico (~3,000 m) |
| Defence | Sequestered cardiac glycosides; aposematic colouring |
| Egg to adult | About 30 days |

## Scientific classification
- **Kingdom:** Animalia
- **Phylum:** Arthropoda
- **Class:** Insecta
- **Order:** Lepidoptera
- **Family:** Nymphalidae
- **Genus:** Danaus
- **Species:** Danaus plexippus

## Conservation status
- **Status:** Vulnerable (migratory subspecies) / Least Concern (species)
- **Population:** Overwintering area is the standard index; counts fluctuate sharply between years
- **Trend:** Long-term decline in the migratory North American population
- **Assessed:** 2022 (migratory monarch); species reassessed Least Concern
- **CITES:** Not listed
- Monarch abundance is reported as hectares of occupied overwintering forest rather than as a headcount. Single-season swings are large, so trends matter more than any one year.

## Key facts: Monarch Butterfly
- Monarchs are famous for migration, but their limiting factor is milkweed, the only plant their caterpillars can eat.
- The migratory subspecies is assessed Vulnerable; monarchs as a species remain widespread and Least Concern.
- The overwintering generation lives around eight months — roughly ten times longer than a summer monarch.
- Caterpillars sequester milkweed toxins, which is why the adult's warning colours work.
- Overwintering sites are tiny in area, so forest loss or a severe storm can hit a huge share of the population at once.
- Planting locally native milkweed and pesticide-free nectar flowers is the single most useful thing a garden can do for them.

## The migration, generation by generation
Monarchs east of the Rockies funnel south each autumn to roughly a dozen oyamel fir groves in Michoacán and the State of México, at around 3,000 m altitude. The cool, humid mountain air keeps them in a low-energy state without freezing them. Western monarchs make a shorter journey to coastal groves in California.

The butterflies that fly south are a distinct 'super generation' — reproductively delayed and long-lived. In spring they head north, breed on emerging milkweed and die; their offspring continue north, and so on, until autumn triggers another super generation. Each individual is navigating a route it has never flown, using a time-compensated sun compass and, in cloud, a magnetic sense.

## Milkweed: the whole story in one plant
A female monarch lays single eggs on the underside of milkweed leaves. The caterpillar hatches, eats the leaf and grows through five instars in about two weeks, taking in cardiac glycosides that make it toxic to most vertebrate predators. It then pupates into a jade-green chrysalis rimmed with gold, and emerges as an adult roughly ten days later.

This is why milkweed availability, not nectar availability, drives monarch numbers. Agricultural intensification, roadside spraying and herbicide-tolerant cropping have removed enormous areas of milkweed from the North American breeding range. Adults will feed on many flowers; caterpillars will starve on anything but Asclepias.

## Why the numbers fell
Three pressures stack. Breeding-habitat loss removes milkweed. Overwintering-habitat loss and degradation — illegal logging, thinning that breaks the forest microclimate — puts the whole eastern population at risk in a very small area. And climate volatility brings storms, freezes and droughts that can kill millions of clustered butterflies in a single event, or shift the timing of milkweed emergence out of step with arriving monarchs.

Insecticides, particularly systemic neonicotinoids present in plant tissue, add a further pressure on both caterpillars and adults. Counts fluctuate sharply year to year, so single-season figures should be read as part of a trend, not as a verdict.

## What actually helps
Plant milkweed native to your own region — not tropical milkweed outside its range, which can keep monarchs breeding too late in the season and sustain the parasite Ophryocystis elektroscirrha. Pair it with a long succession of pesticide-free nectar flowers so migrating adults can refuel.

Beyond the garden, the leverage is in protecting overwintering forest, keeping field margins and roadside verges unsprayed, and supporting the community forestry that makes protection viable for people living beside the reserves. Captive rearing and mass release is popular but contested: it can spread disease and does nothing about the missing habitat.

## What WARN does
WARN publishes free, sourced wildlife education so that the animals people already love become an entry point into the pressures facing wildlife everywhere. Insect decline is the least visible part of the biodiversity crisis and the part most directly shaped by everyday choices — what gets planted, what gets sprayed and what gets left alone.

If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.

## Frequently asked questions: Monarch Butterfly
### Are monarch butterflies endangered?
Not as a species. Monarchs are widespread and assessed Least Concern globally. The migratory monarch of North America (Danaus plexippus plexippus) was assessed as Vulnerable by the IUCN in 2022 because of losses in breeding and overwintering habitat and the risk concentrated at its few overwintering sites.

### Why do monarch caterpillars only eat milkweed?
Monarchs have evolved to tolerate the cardiac glycoside toxins in milkweed (Asclepias) and to store them in their own tissue as a defence. That specialisation means the caterpillars cannot digest other plants — no milkweed, no monarchs, regardless of how many nectar flowers are available.

### How far do monarch butterflies migrate?
Eastern North American monarchs travel up to about 4,000 km to overwintering forests in central Mexico. Western monarchs make a shorter migration to coastal California. No individual completes a full round trip — it takes three to four generations.

### How long do monarch butterflies live?
A summer-generation monarch lives roughly two to six weeks. The autumn 'super generation' that migrates and overwinters delays reproduction and can live around eight months.

### What is the best way to help monarch butterflies?
Plant milkweed species native to your own area, add pesticide-free nectar flowers that bloom across the whole season, and avoid systemic insecticides. Supporting protection of the Mexican overwintering forests addresses the risk concentrated at the other end of the migration.

### What do monarchs eat?
Monarchs eat Milkweed (Asclepias spp.) only. The monarch butterfly (Danaus plexippus) is an orange-and-black North American butterfly whose migratory population travels up to 4,000 km to overwinter in Mexican fir forests; the migratory subspecies is listed Vulnerable, and it breeds only on milkweed.

### Where do monarchs live?
Monarchs live in North America, Central America — Mexican overwintering forests, Introduced populations in Australia, New Zealand and Iberia. The monarch butterfly (Danaus plexippus) is an orange-and-black North American butterfly whose migratory population travels up to 4,000 km to overwinter in Mexican fir forests; the migratory subspecies is listed Vulnerable, and it breeds only on milkweed.

### Are monarchs dangerous?
Monarchs are not generally dangerous to people. The monarch butterfly (Danaus plexippus) is an orange-and-black North American butterfly whose migratory population travels up to 4,000 km to overwinter in Mexican fir forests; the migratory subspecies is listed Vulnerable, and it breeds only on milkweed. Give wild individuals space and do not corner or handle them.

### How big is a monarch?
A Monarch is about 8.9–10.2 cm. The monarch butterfly (Danaus plexippus) is an orange-and-black North American butterfly whose migratory population travels up to 4,000 km to overwinter in Mexican fir forests; the migratory subspecies is listed Vulnerable, and it breeds only on milkweed.

## Sources
- [IUCN Red List — Danaus plexippus plexippus](https://www.iucnredlist.org/species/194052138/200522253)
- [IUCN Red List — Danaus plexippus](https://www.iucnredlist.org/species/159971/219149911)

---
Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/monarch-butterfly