A month or so ago, I came across this caterpillar. It was chewing its way through willow leaves on plants near the edge of the pond. It’s a Viceroy (Limenitis archippus) caterpillar. The Viceroy caterpillar is one of a few species who are often compared to bird droppings. The Red-spotted Purple butterfly (Limenitis arthemis astanax) also has bird-dropping-like caterpillars.
I wrote a bit about Viceroys when I spotted one at the Upper Canada Bird Sanctuary back in June. Recently, there have been a number of Viceroys on the wing around the house, visiting the hydrangea and other flowers. Presumably, some of them were once caterpillars on the willows by the pond. Here’s a quote from that earlier post:
The Viceroy (Limenitis archippus) looks like a small Monarch butterfly. It can be readily differentiated by its smaller size and by the black line that runs across the bottom of the lower, or hind wing, lacking in the Monarch. The larvae of Monarchs feed mostly on milkweeds. Chemicals derived from the milkweed make Monarchs very distasteful to most predators. It was once believed that the Viceroy was a Monarch mimic so that it might take advantage of this predator protection scheme, but it is now thought the Viceroy is equally distasteful to predators. The larval food for the Viceroy is willow species.
A good source of information about the life cycles of the most common butterflies is Burris and Richards’ aptly-named book, The Life Cycles of Butterflies. Below is the double-page spread on Viceroys.