Brood XIX (also known as The Great Southern Brood) is the largest (most widely distributed) brood of 13-year periodical cicadas, last seen in 2011 across a wide stretch of the southeastern United States. Periodical cicadas (Magicicada spp.) are often referred to as "17-year locusts" because most of the known distinct broods have a 17-year life cycle. Brood XIX is one of only three surviving broods with a 13-year cycle. It is also notable because it includes four different 13-year species, one of which was discovered in Brood XIX in 1998 by scientists listening to cicada songs. Position among other broods of cicadas Every 13 years, Brood XIX tunnels en masse to the surface of the ground, mates, lays eggs, and then dies off in several weeks. In 1907, entomologist C. L. Marlatt postulated the existence of 30 different broods of periodical cicadas: 17 distinct broods with a 17-year life cycle, to which he assigned Roman numerals I through XVII (with emerging years 1893 through 1909); plus 13 broods with a 13-year cycle, to which he assigned Roman numerals XVIII through XXX (1893 through 1905). Many of these hypothetical broods, however, have not been observed. Today only 15 are recognized. Brood XIX is one of three extant broods of 13-year cicadas. The other two are Broods XXII and XXIII, expected to re-emerge in 2027 and 2028 respectively. A fourth 13-year brood, Brood XXI (The Floridian Brood) was last recorded in 1870 in the Florida panhandle, but is believed to be now extinct. Species present Brood XIX includes all four different species of 13-year cicadas: Magicicada tredecim (Walsh and Riley, 1868), Magicicada tredecassini (Alexander and Moore, 1962), Magicicada tredecula (Alexander and Moore, 1962), and the recently discovered Magicicada neotredecim (Marshall and Cooley, 2000). 2011 is the first appearance of Brood XIX since the discovery of the new species, which was first observed in this brood in 1998 when scientists observed an unexpected peak of acoustical frequencies in the brood's song. The two species M. tredecim and M. neotredecim have an unusual geographical relationship in Brood XIX, with only a slight overlap between them, in a narrow band from northern Arkansas to southern Indiana. The other 13-year species occur together throughout the brood range, so in most parts of the range only three of the four species are present. All four 13-year species have distinct male calling songs, but the songs of M.