With all of the strange weather and eastern winds, the monarch migration still hasn't really gotten started here in Cape May. If the forecast stays the same, next Wednesday (Sept. 19th) is looking good for weather and winds. Fingers crossed for an influx of migrants! Until then, I wanted to share some images and information on a monarch butterfly lookalike, or mimic: the viceroy butterfly.
Monarch on Butterflybush |
Mimicry in the Animal Kingdom
For many years, it was thought that viceroy butterflies were
Batesian mimics of monarchs. Batesian mimicry is when a palatable species
evolves to resemble an unpalatable species to avoid being eaten. Since they are
not poisonous themselves, they can at least appear to be so in order to “trick”
predators into thinking they are the poisonous species they evolved to look
like.
However, in recent studies, it was found that the viceroy
butterfly is in fact unpalatable to predators. When caterpillars, viceroys eat
plants in the willow family (Salicaceae) and keep the salicylic acids in their
bodies through adulthood, which makes them inedible to vertebrate predators. Monarchs, as
many may know, do the same with sequestering toxins out of milkweed. Since both
butterflies are toxic to vertebrate predators, their relationship is no longer Batesian
mimicry. This type of mimicry is known as Mullerian mimicry, where both species
are unpalatable and evolved to mimic each other. This is an
advantage for both species since fewer individuals of a species have to die in
order for the predators to learn to avoid them.
To tell the difference between a monarch (image below on left) and viceroy (image below on right), there
are multiple things you can look at. What you will likely notice first is the
size difference. Monarchs have a wingspan between 94 and 105mm, and viceroys
have a wingspan between 53 and 81mm. These butterflies do not need to be seen
up close to notice this size difference, and the images below help emphasize how much
larger the monarchs really are.
Even though the butterflies share the same coloration, the
patterns of the dark lines differ in each of the wings. On the outsides of the hind
wings, viceroys have an additional black line going perpendicular across all of the
radial lines. Monarchs lack that perpendicular black vein. This
additional line on the viceroy is the most distinctive difference between
these mimics.
[Post by Field Naturalist Sarah Crosby]
Viceroy |
Monarch |
[Post by Field Naturalist Sarah Crosby]
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