The eight moths investigated are (1) Gnorimoschema gallaesolidaginum (Riley), (2) G. jocelynae N. Sp., (3) G. salinarum Busck, (4) G. septentrionellum Fyles, (5) G. gallaespeciosum N. Sp., (6) G. gibsoniellum Busck, (7) G. slabaughi N. Sp., and (8) G. gallaeasterellum (Kellicott). Little or no information has hitherto been available for five of them. Coverage includes adult and gall traits, distribution point maps, insect biology, gall biology, diagnostic characters of adults and galls, and intra- and intersite incidence. Study material consisted mostly of galls I collected, adults that issued from them, and gall data from many old-field sites in Ohio, Maryland, Michigan, Minnesota, and elsewhere. Distributions range from localities in two states for gall moth No. 5 to trans-Nearctic for No. 1. These taxonomically similar gallers are univoltine, with adults eclosing in late summer, and unhatched pharate larvae overwintering. Larval foodplants include species of Solidago, Aster, Grindelia, and Haplopappus (Asteraceae), on all of which the moths are monophagous to oligophagous. Foodplant ramets are selected by neonate larvae. Typically, young larvae bore downward through the pith, molt, reverse direction of travel, molt again, then concentrate feeding and gall-induction. The fusiform, monothalamous galls are vertically symmetrical to pear-shaped. The extended phenotype concept of Dawkins enabled certain gallers to be unequivocally distinguished by gall traits, notably by the intricate architecture of the larval-prepared adult exit. Adult exits of galler Nos. 1–3 are plugged with distinctive bungs. Galler No. 2, a widespread cryptic and sibling species to No. 1, was discovered by its differing adult exit architecture. Adult exits of the bungless gallers are capped with intact plant epidermis, or with plant tissue fragments interwoven with silk. I provide a key for distinguishing the eight gall moths that integrates insect and gall characters.