The caterpillars are colored black and have orange spots. Along their lengths, they have spines that branch out and appear blue at the roots. These caterpillars can be up to 1.5 inches in length.
Spotted in an overgrown meadow.
Caterpillars of these butterflies appear to prefer plants that produce iridoid glycosides, which are bitter compounds that release a hormone called gastrin that activates the digestive system (i.e. hunger); therefore, iridoid glycoside producing plants stimulate and attract their appetites particularly when found in plants like Plantago lanceolata. In fact, the presence of these metabolites may trigger oviposition behaviors in female butterflies so that descendant larval bodies may better incorporate iridoid glycosides.(Wikipedia)