Hey, lay off the viceroy!

The viceroy butterfly had a bad rap for far too long. Here’s how researchers cleared its name.

The viceroy butterfly was long understood to be a good-tasting copy-cat of the foul-tasting monarch butterfly. In reality, the viceroy tastes just as bad to birds as the monarch does. A third species, the queen butterfly, is actually the tastiest species in this trio of orange-and-black butterflies.

Mimicry 101

Mimicry is often cited as an example of evolution by natural selection. When predators eat prey that taste bad, they may remember what that prey looked like and avoid eating it in the future. When multiple foul-tasting species look similar, it reinforces the message to predators to avoid prey that look like that group of species. If bitter species look different than the prey the predators have learned to avoid, their bitter defenses will do them less good as predators try to eat them before realizing they taste bad. So, bitter prey are selected to look similar. This type of mimicry, when all animals in a mimicry group taste bad, is called Müllerian mimicry.

Other, good-tasting prey species may be selected to express color coordination that allows them to blend in with the bad-tasting group of species. Predators avoid prey that look like foul-tasting species, so even good-tasting species will survive and reproduce more successfully if they look like the bad-tasting species. This way, they benefit from other animals’ bad-tasting chemical defenses without expending energy maintaining the bitter chemicals themselves. This kind of mimicry, when an animal looks like a chemically defended group of animals without actually having those defenses, is called Batesian mimicry.

Animals with chemical defenses are called ‘models,’ while un-defended copiers are called ‘parasitic mimics.’

False accusations

Historically, it was thought that the viceroy butterfly (Limenitis Archippus) was a parasitic mimic benefitting from the chemically defended queen (Danaus gilippus) and monarch (Danaus plexippus) butterflies.

Zoologists Ritland and Brower put this idea to the test in 1991. Using wild-caught male red-winged blackbirds as ecologically relevant predators, researchers presented the birds with only the abdomens of different butterflies. This way, the birds would react based on taste alone, without wing color to distract them. Previous studies had shown that the taste of the abdomen is a good representative of the taste of the entire butterfly. Each bird received 8 monarch, 8 viceroy, 8 queen, and 24 palateable control abdomens.

Not only were viceroys significantly less palateable to the birds than control butterflies, they were the most unpalateable species. Only 41% of viceroys were eaten compared with 98% of controls. Birds commonly acted disgusted after tasting a viceroy, shaking their heads, drinking lots of water, and looking agitated. This shows that viceroys are certainly not palateable mimics in this mimicry group.

Setting the record straight

While monarchs and viceroys were similarly distasteful, queens fell behind. 68% of queens were eaten, significantly more than viceroys or monarchs.

This means the queen butterfly benefits more from its orange outfit than the viceroy does, reversing the previously accepted roles of mimic and model.

Overall, the three butterfly species share similar wing patterns and foul tastes. All three benefit from predators learning to avoid orange-and-black butterflies, making the group an example of mullerian mimicry. But, the queen benefits more from this mimicry than the viceroy or the monarch does.

Classical interpretation had painted the viceroy as a dishonest scoundrel posing to be as distasteful as a monarch or queen butterfly and avoiding predation at their expense. Now, we know this accusation was unfounded.

Like me, you may have learned in school that the viceroy was a sweet-tasting mimic flying under the radar. If so, then forget what you thought you knew about the viceroy. In a world of queens and monarchs, the viceroy wears the foul-tasting crown.

Reference:

Ritland, D.B., and Brower, L.P. (1991). The viceroy butterfly is not a batesian mimic. Nature, 350, pp. 497-498. DOI: https://doi.org/10.1038/350497a0

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