Card #099 · Invertebrates
Monarch butterfly (migratory population)
Danaus plexippus plexippus
Super Rare VU · Vulnerable
Field notes
- Classification
- Order Lepidoptera · Family Nymphalidae
- Range
- North America (migratory)
- Size
- 9–10 cm wingspan
- Weight
- ~0.5 g (0.02 oz)
- Lifespan
- 2–5 wks (to 8 mo)
- Diet
- Milkweed, nectar
Most Notable
Each autumn they stream up to 4,000 km to a few mountain groves in central Mexico. No one butterfly survives the round trip; it takes three or four generations, yet each finds the same forests its ancestors did.
Its caterpillars eat only milkweed, storing the plant's bitter poisons in their own bodies; the adult's bold orange and black is a warning that it is toxic to eat, a signal so effective that other butterflies have evolved to mimic it.
The migratory monarch was listed as Endangered by the IUCN in 2022, then reassessed to Vulnerable in 2023; either way, its overwintering colonies have shrunk dramatically over recent decades.
At their Mexican wintering sites monarchs gather in the millions, clustering so thickly on the oyamel firs that whole branches bend under their weight and the trees seem to turn orange.
Most monarchs live only a few weeks, but the special generation born in late summer delays breeding, lives up to eight months, and is the one that makes the long flight south.
Range: Breeds across North America; winters in central Mexico.