Monarch butterfly

The orange-and-black butterfly whose fall generation flies thousands of miles to the same winter trees, feeding only on milkweed as a caterpillar.

Monarch butterfly at a glance

Danaus plexippus MON-ark; Danaus plexippus is DAN-ay-us plex-IP-us

Type
Invertebrate · butterfly
Diet
Herbivore
Size
Its open wings stretch about 4 inches across (about 10 cm), roughly as wide as a playing card is long. The whole butterfly weighs less than a paperclip.
Lifespan
Most adults live only about 2 to 5 weeks. But the special generation born in late summer lives about 8 to 9 months, long enough to fly south, wait out winter, and start back north in spring.
Conservation
Migratory monarch: IUCN Vulnerable (Endangered in 2022, reassessed to Vulnerable in 2023); proposed for U.S. Endangered Species Act listing as Threatened in 2024, not yet finalized

Eats milkweed leaves (as a caterpillar), flower nectar (as an adult)

As a caterpillar, a monarch eats only milkweed leaves. The milkweed holds bitter chemicals called cardenolides that stay in the monarch's body and make it taste terrible to birds. As an adult, it uncoils a long, straw-like tongue to drink nectar from flowers.

Should you worry?

None. A monarch cannot bite or sting. Its poison only works on animals that try to eat it, like birds, and even then it just makes them sick. Holding one gently will not hurt a person. The kind thing is to look and not grab, because their wings tear easily.

The monarch is easy to know by its orange wings veined in black, but the color is more than decoration. As a caterpillar the monarch eats only one thing, milkweed, and the plant carries bitter chemicals called cardenolides that stay in the body all the way into adulthood. A bird that tries a monarch gets a mouthful of that bitterness and learns to leave the orange butterfly alone. The grown monarch trades its leaf-chewing mouth for a long, coiled tongue and drinks nectar from flowers instead.

What makes a monarch remarkable is the trip. Most monarchs live only two to five weeks, but the generation born in late summer is different: it lives eight or nine months, and it flies. Those butterflies leave the northern states and Canada in fall and travel as far as three thousand miles to the same groves their great-great-grandparents used, in the mountains of Mexico or along the California coast near Pinnacles and the Channel Islands. No single butterfly makes the round trip. It takes three or four shorter-lived generations to work back north the next spring.

The traveling monarch is in trouble. Scientists moved it from Endangered to Vulnerable in 2023, a change in the math rather than a real recovery, and the U.S. government has proposed protecting it as a threatened species. A monarch cannot bite or sting, and its poison only troubles an animal that tries to eat it, so a person can watch one up close in complete safety. The wings tear easily, though, so be gentle: look, and let it fly.

Did you know?

  • No single monarch makes the whole round trip. The butterflies that leave the northern United States and Canada in fall fly up to about 3,000 miles to the same groves in Mexico or along the California coast. It then takes three or four shorter-lived generations to travel back north the next year.
  • A monarch caterpillar eats only milkweed. The plant's poison stays inside the grown butterfly, so its bright orange color works as a warning sign that tells birds it will taste awful.
  • In winter, monarchs pile onto the same trees and hang in clusters so thick the branches bend. Along the California coast they gather at groves near Pinnacles and the Channel Islands.

Common questions

Are monarch butterflies poisonous to kids?

No. Their poison only bothers animals that eat them, like birds. You can watch or gently hold one without getting hurt. Their wings are fragile, so be careful.

What do monarch caterpillars eat?

Only milkweed leaves. Milkweed is the single plant a monarch caterpillar will eat.

Where do monarchs go in winter?

They fly south to warm groves, in Mexico or along the California coast, and cluster together on trees until spring.

How far can a monarch fly?

The fall generation can travel up to about 3,000 miles to reach its winter home.

Are monarchs endangered?

The traveling kind is in trouble. Scientists now call it Vulnerable, and the U.S. government has proposed protecting it under the law for threatened animals.

Where it lives

Where we got this