Adults emerge in early spring as host plants begin to bolt. Adults are up to 5 mm long and have gray bodies with dark-spotted abdomens and yellow-orange legs. The wings are clear with three black marks along the leading margins and fainter marks on hind margins. Eggs are laid in immature female seed heads of Canada thistle. Larvae feed on seeds and receptacle tissue. They are white maggots that develop through three instars are up to 6 mm long at maturity. Just before seeds begin to disseminate, larvae form cocoons of tangled pappus hairs in which they overwinter. Pupation occurs in spring, and there is one generation per year.