Monarchs, Viceroys and Queens

 

A Monarch Butterfly (Danaus plexippus) feeding on 
Tropical Milkweed (Asclepias curassavica).
Rowan County, North Carolina.

I know, I know, another story about Monarch Butterflies.  I can’t help it.  Monarchs (Danaus plexippus) are large, brilliantly colored, poisonous and make an epic migration every year. Monarchs also belong to a mimicry complex, a group of butterflies that resemble each other.  This resemblance protects them from predators.  Monarchs are distasteful to birds because their larvae develop on milkweeds (Asclepias sp.).  Milkweeds make toxic compounds called cardiac glycosides that repel most insects but the Monarch larvae have evolved tolerance to these chemicals.  When a Monarch larva metamorphoses into the adult butterfly it retains the toxic plant compounds to repel birds. 

 

Monarch Butterflies migrating through the Black Mountain Gap below
Mount Mitchell, North Carolina.  These Monarchs were feeding on Aster sp. 
on their way to Mexico.  Yancy County, North Carolina.

Viceroys (Limenitis archippus) and Queens (Danaus gilippus) both bear a remarkable resemblance to Monarchs with their bright orange wings, striped with black and dotted with white.  Monarchs are found throughout North America and into Mexico.  Viceroys live in the eastern two thirds of North America and Mexico.  Queens have a more southern distribution along the southern border states of the US from Florida to California and into Mexico. 

 

A Viceroy Butterfly (Limenitis archippus) resting on a Tag Alder
(Ulnus serrulata). Viceroys and Monarchs are members of a mimicry complex.
Clayton County, Georgia.

The standard story of mimicry in these butterflies has the Monarchs being protected from bird predators by toxic cardiac glycosides.  Viceroys were supposed to be palatable to birds and avoid being eaten because of their resemblance to Monarchs even though they don't have chemical protection.  This type of mimicry, with a toxic model (Monarch) and a tasty mimic (Viceroy) is called Batesian mimicry.  Henry Walter Bates, a 19^th Century English naturalist who is the namesake for this mimicry, first described this relationship based on his study of South American butterflies. 

Recently researchers have shown the Monarch-Viceroy mimicry story is more complicated than originally thought.  Viceroy butterfly larvae often develop on willow (Salix sp.) leaves and can also be poisonous.  Willows contain toxic salicylic compounds related to aspirin.  The Viceroy caterpillars ingest these molecules and the adult butterflies may be unpalatable to birds.  Mimicry where two protected species resemble each other is called Müllerian mimicry, named for German zoologist Johann Müller.   Müller, like Bates, studied butterflies in South American in the 1800s and discovered this distinctive type of mimicry.  In Müllerian mimicry several protected species resemble each other and all are protected from predators.  Müllerian mimicry is why bees, wasps, yellow jackets and hornets all resemble each other. The yellow and black bodies of these insects send a clear message to leave us alone.  Monarchs and Viceroys (sometimes) are both chemically protected so their resemblance can be Müllerian mimicry.  

 

A Queen (Danaus gilippus) feeding on Oakleaf Fleabane (Erigeron quercifolius).
This butterfly is also a member of the mimicry complex with Monarchs and Viceroys.
Palm Beach County, Florida.  

Queens are closely related to Monarchs and their larvae develop on milkweeds and their relatives.  Queens are protected by the same cardiac glycosides found in Monarchs.  Viceroys were once thought to be Batesian mimics of Queens where their ranges overlap.  But since we now know Viceroys are chemically protected this is another example of Müllerian mimicry.   The Viceroy-Queen story in Florida is even more complicated.  In 2019 a group of American researchers found that in north Florida the Viceroy population is high and the Queen population is low.  There the Viceroys have a higher concentration of chemical defense compounds.  In south Florida Queens are abundant and Viceroys are rare and are not well protected.  But in central Florida both species are relatively abundant and the Viceroys have low concentrations of their protective chemicals.  With lots of Queens around, the Viceroys do not need as much of the toxic chemicals.  So, in central Florida, the Viceroy-Queen relationship changes from Müllerian to Batesian mimicry.  

 

A Monarch on Tropical Milkweed. 
Rowan County, North Carolina.

The work of both Bates and Müller on mimicry gave early, independent evidence for Darwin and Wallace’s theory of Natural Selection. This mimicry is on display for us to see in these brilliant butterflies.