Overwintering adults emerge in spring and oviposit on Canada thistle stems and leaf undersides. Adults are dark metallic-blue, up to 5 mm long, and have narrow heads, bulging eyes, and long segmented antennae. Larvae feed on the undersides of leaves while the upper epidermis remains intact, forming a characteristic feeding window. Mature larvae drop to the soil in midsummer, pupating within cocoons made of foam they secrete. Adults emerge in late summer and feed on Canada thistle foliage prior to overwintering in soil.