The geographical distribution of Smicra differs much from that of Leucospis. Unlike the latter genus, which is spread thinly and somewhat equally over the warm and temperate regions of the earth, Smicra, with very few exceptions, is limited to the New World, where there are some species in North America, many in Mexico and in the West Indies, and great abundance in the tropical parts of South America, and the genus has thus much more influence than Leucospis in regulating, by means of transfer, the increase of other insect tribes.