Monarch Lookalikes and How to Tell the Difference

"Imitation is the sincerest form of flattery."- Oscar Wilde
​...Or was it mimicry?

At a glance, the Viceroy and Monarch are shockingly similar with their orange and black wing coloration. This is not merely a coincidence but a means of survival for these butterflies. There is a name for this phenomenon called Müllerian mimicry- “a form of mimicry in which two or more noxious animals develop similar appearances as a shared protective device”.
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It was long believed that the Viceroy used Batesian mimicry- “mimicry in which an edible animal is protected by its resemblance to a noxious one that is avoided by predators.” However, it was found that the viceroy feeds on Willow species (cottonwood, willow, poplar trees) which contain salicylic acid, the active ingredient in aspirin and make them taste bitter to avian predators. 

Viceroy or Monarch?

The main visual difference between the viceroy and monarch butterfly is the black line drawn across the viceroy's hind wings, which monarch butterflies do not have. The viceroy is also a bit smaller than the monarch. The caterpillars of monarchs and viceroys are significantly different in appearance as well. 

An adult monarch butterfly

An adult viceroy butterfly. Note the black line across it's hind wing, differentiating it from the monarch.

The viceroy caterpillar doesn't look anything like the monarch caterpillar

Why is it important to be able to tell the difference between the two?

1. Citizen science is only helpful if the data is accurate. Monarch populations are in decline and it is important to be able to report sightings in order to gather data on their migration cycle.
2. Planning your butterfly garden. Viceroys feed on all plants in the willow family, but the females will also deposit eggs on plums, apples and cherries. Monarchs feed and reproduce solely on Milkweed.
3. It’s fun and educational! You can impress your peers by being able to aptly identify different kinds of butterfly and also be able to share this knowledge with others to increase conservation efforts. ​

Why does the monarch taste bad to predators?

The monarch is unpalatable to its predators because it feeds on milkweed as a caterpillar which contains toxic cardiac glycosides. It’s brightly colored wings also serve as a warning sign of its toxicity to its predators.

Other lookalikes

The queen butterfly (Danaus gilippus) has white spots on its hind wings, distinguishing it from the monarch. It is also a darker color orange than monarchs. During the caterpillar phase, however, the monarch and queen are very similar.

Here is a picture of a queen caterpillar on top and a monarch caterpillar on bottom. They are closely related and in the same genus (Danaus). Queen butterflies do not migrate.

Soldier butterfly (Danaus eresimus) is a cousin to the monarch (Danaus plexippus). It is a darker orange than the monarch and has white spots on its wing borders. It is also smaller than the monarch.