Harmless to handle. It stores cardenolides from milkweed that make it toxic to eat, which matters to a bird and not to you — there is no sting, no bite and nothing that reacts with skin.
SizeWingspan 90–105 mm
MarkingsDeep orange with heavy black veins and a black border studded with white dots · No black line crossing the hindwing veins — that line means a viceroy
WhereAnywhere milkweed grows — meadows, roadsides, gardens, field margins and prairie.
SeasonSpring through autumn, with the migratory generation moving south from August
How to tell it apart
Deep orange with heavy black veins and a black border studded with white dots
No black line crossing the hindwing veins — that line means a viceroy
Males carry a black scent patch on a vein of each hindwing
Wingspan 90–105 mm, and a slow sailing flight rather than a flutter
Caterpillar is banded yellow, white and black, always on milkweed
Where you’ll find it
Across the United States. Eastern populations overwinter in central Mexico, western ones along the California coast.
Anywhere milkweed grows — meadows, roadsides, gardens, field margins and prairie.
Spring through autumn, with the migratory generation moving south from August.
How it behaves
The migration is the thing that makes it famous and it is stranger than usually told: no individual completes the round trip. Three or four short-lived summer generations move north, then a single long-lived autumn generation flies the whole way to Mexico, overwinters, and starts back. The caterpillars eat only milkweed, which is where the toxins come from and why both the larva and the adult can afford to be brightly coloured rather than hidden.
You’ve found one indoors
If you want monarchs, plant milkweed native to your region and stop cutting it. That single measure does more than anything else available. Rearing them indoors in numbers is popular and increasingly discouraged — it spreads disease and produces weaker migrants than wild-reared ones.
Common questions
How do I tell a monarch from a viceroy?
One black line. A viceroy has a black band crossing the veins of the hindwing; a monarch does not. The viceroy is also noticeably smaller.
Are monarchs poisonous?
To eat, yes — they carry cardenolides from milkweed and a bird that tries one is usually sick and does not repeat it. They are completely safe to handle.
Does one butterfly fly all the way to Mexico and back?
No. The autumn generation flies south and overwinters, but the return north is completed by its descendants over several short-lived generations.
Should I raise monarchs indoors?
Conservation guidance has moved against rearing them in quantity. Captive conditions spread parasites and appear to produce butterflies that migrate less successfully. Planting milkweed helps more.
Jon Sullivan · CC-BY