The slightest thing will send me off to Google. Sometimes it's boring, but very often it's fascinating. All the monarch posts lately reminded me of something I learned a long time ago - that the monarch butterfly has a mimic. The mimic is called the viceroy butterfly, and they look incredibly similar:
More images to compare here.
Now the original theory on this was that the monarchs dine on milkweed, which contains toxins. The monarchs are immune, but the toxins are unpalatable and/or toxic to their predators. The bright colors and distinctive pattern allow predators to spot the monarchs and avoid them.
There are many types of mimicry in nature. It was always assumed that the viceroys were using something called Batesan mimicry. Predators avoid eating things that look like monarchs, so the more you look like a monarch, the less likely you are to be eaten.
But a study was done that indicated that viceroys were just as unpalatable as monarchs. They are now classified as Mullerian mimics, where two species adopt a common appearance, so that predators only have to distinguish one pattern instead of multiple patterns.
But wait, there's more... The viceroy is apparently the Rich Little of the butterfly world. Both the caterpillar and the chrysalis have the appearance of bird droppings. In some regions, a relative of the monarch called the queen butterfly is more common. This source says that in regions where the queen is more common, "the white spotting of the viceroy becomes less noticeable, and the orange coloration is replaced by a deep mahogany brown."
Ain't nature fascinatin'?