Very similar in life cycle to its close relative Chrysolina hyperici. Larvae emerge in early spring and feed on young foliage when plants begin growing. Ingesting common St. Johnswort makes larvae photosensitive, so most feeding occurs before sunrise. They develop through four instars, and pupation occurs in the soil in late spring. Adults emerge as common St. Johnswort plants bolt and begin budding in spring and summer. Adults feed through early summer then drop to the soil and enter an obligate period of rest, called aestivation. In response to shortening day length, adults return to plants and resume feeding on foliage in the fall, laying eggs on basal re-growth of common St. Johnswort. This species primarily overwinters as eggs. At some locations, including places with insufficient fall moisture, adults overwinter and lay eggs in spring. Eggs usually hatch in early spring, but in mild climates, fall-hatched larvae can survive the winter. There is one generation per year.