The genus Locusta, L. (= Pachytylus, Fieb.) includes two of the most destructive swarming locusts of the Old World: the widely distributed L. migratoria, L. (with L. danica, L., and L. migratorioides, Rch. & Frm., as its forms; see below), and the South African L. pardalina, Walk. The literature on the economics, biology and especially on the means of control of these locusts is enormously extensive, but at the same time their systematic arrangement is in considerable confusion, and extremely contradictory opinions as to the mutual relationship of the different so-called species exist among specialists. As a direct consequence of this, the field research and control work of economic entomologists is apt to suffer through the difficulty in getting a particular species properly named, and thus it is often impossible to make a comparison of the records as to the biology and control of the same species in different countries.