THE EGG-SAC IN THE IDENTIFICATION OF SPECIES OF LATRODECTUS (BLACK-WIDOW SPIDERS)

The genus Latrodectus comprises a few species very hard to classify. The geographical distribution of some spreads across several continents, making the problem even more complex and, at the same time, the synonymy richer. The difficulty lies in the lack of taxonomic characters which allow true differentiation among the species. Levi (959) used for species identification, among other devices, the male genitalia as well as the female; thanks to this the problem of systematics of so. ill-treated a group begins to be clearer. In the course of the research we are carrying out on Latrodectus in Santiago del Estero (north-central region of Argentina) we have recognized the presence of five different species living in the same area. We were able to separate two of them according to their morphological characters; L. jeometricus C. L. Koch, a domestic species we identified by its well-defined color and genitalic characters, among them the coils of the embolus of the male palpus, coils corresponding to those in the connecting ducts of the female. The other species, temporarily named Latrodectus No. in order not to add further confusion of names, resembles L. curacaviensis (Mfiller) in the genitalic characters pointed out by Levi: the embolus of the male palpus and the connecting ducts of the female with two coils. The three remaining species correspond to what we call "’L. mactans complex" with their three coiled embolus and female, ducts. The morphological characters are not enough to separate these species. The width of the red spots on the abdomen guides the identification but is not reliable. The three of them live in the. same area and ecologic environment. The only elements that allow us at present to separate these species in an accurate way are the size, shape and texture of the egg-sacs. We have. temporarily called these species: Latrodectus No. 2, Latrodectus No. 3, and Latrodectus No. 4. However, many names are available for the species. Latrodectus No. 2: The egg-sac is white when just formed, but usually turns yellowish in the course of days; it is spheroidal, slightly 1Research under the sponsorship of Conse]o Nacional de Investlgaciones Cientificas y Tcnicas of Argentina. 2Levi, H. W. 1959. The spider genus Latrodectus (Araneae, Theridiidae)