The habitats and host plants of Euphydryas phaeton in the Great Lakes region are examined using data from several different populations spread over much of the region. The range of habitats and host plants used by this species is wider than commonly believed. While many populations are found in seasonal or permanent wetlands, others are located in dry, old fields or woodland areas. The host plants used vary with habitat, but they include all major primary hosts and many secondary hosts previously reported plus several new records. The biology of E. phaeton is shown to be similar to western Euphydryas butterflies in which variation in habitat and host plant use is well documented.