Mourning Cloak Butterfly Caterpillar and Adult
In the first week of August 2013, Sam and Rosie each found one of these delightful black, spiky caterpillars with orange spots on their backs. They were quite large, over two inches long.
From the side, we can see that they also have orange prolegs.
Identifying these is no trick at all: the only thing that even looks close are the caterpillars of Mourning Cloak butterflies, Nymphalis antiopa.
They weren’t found on their foodplant (around here, they would most likely be on cottonwood, aspen, or birch), which suggested that they were looking for a place to pupate. So, we put them into a cage, and they promptly made these brown, spiky chrysalises:
In this next picture, you can see the caterpillar skin that sloughed off when the chrysalis formed:
They emerged as adults about 2 weeks later. Yep, those are Mourning Cloaks, all right.
Mourning Cloaks are unusual in that they overwinter as adults. They find a protected spot where they can pretend to be a dead leaf or bit of bark all winter, and then fly first thing in the spring. While the top sides of their wings are fairly colorful, the undersides look as much like a piece of bark as one could wish:
They have an unrolling proboscis like other butterflies do, but they don’t generally like to go to flowers for nectar. Probably because the times that the adults are flying are also the times when there aren’t a lot of nectar-bearing flowers available. They prefer juice from rotting fruit (in the fall) and tree saps (in the spring).
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Willows are their main food source here, but have never seen one.
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I found at least 50 of these caterpillars on my corkscrew willow tree this morning….on the Oregon southern coast