I’ve written about this subject once before, shortly after moving here. However, I have better photos of a White Admiral now, and it’s a cool enough topic to be worth talking about twice!
Here are a couple photos I took yesterday of a White Admiral, Limenitis arthemis.
Here’s a photo I took in Ohio two years ago of a Red-spotted Purple… ALSO Limenitis arthemis.
Yep, these are two populations of the same species, which my field guide suggests could be collectively referred to as the Red-spotted Admiral, although no one actually uses that name. This is a fantastic example of Batesian mimicry, where a tasty species mimics an unpalatable one to get predators to leave it alone. In the southern parts of Limenitis arthemis‘s range, it overlaps with another butterfly, the poisonous Pipevine Swallowtail.
So, it mimics the swallowtail’s iridescent blue wings. Further north, though, where there aren’t any Pipevine Swallowtails, what’s the point? So they revert to their white-striped wing pattern instead. Where the two populations meet, you can find butterflies with intermediate markings.
The “White-spotted Admiral” is in the same genus as that other, better-known mimic butterfly, the Viceroy (Limenitis archippus), which looks almost exactly like a Monarch – except in the western part of its range, where another nasty-tasting milkweed butterfly, the Queen, is more common. Out there the Viceroy looks like a Queen instead. However, the Viceroy is not a Batesian mimic, but a Müllerian mimic, meaning its warning colors aren’t a deception. The Viceroy is just as bad-tasting as the butterflies it imitates, and sharing their warning colors helps reinforce the message (kind of like how a wide variety of stinging insects share a pattern of black and yellow stripes).
To sum it all up: natural selection is really cool!