During Spring 2012 in Indiana, we were visited by large numbers of Question Mark Butterflies, Polygonia interrogationis. These butterflies overwinter as adults. The unusually mild conditions in winter of 2012 may have led to larger than normal survival. The adults lay their eggs on a variety of plants including elm hackberry and nettle. The eggs are laid in clusters.
Caterpillars of the question mark butterfly look formidable with large branched spines for protection from predators. Host plants such as stinging nettle may deter many vertebrate predators from investigating the immediate habitat. There are typically two generations each year in Indiana. Caterpillars can be found by closely inspecting stinging nettle for feeding damage.
Question Mark Caterpillar on Stinging Nettle.
Living With Insects Blog 
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