THE EGG-SAC IN THE IDENTIFICATION OF SPECIES 
OF LATRODECTUS (BLACK-WIDOW SPIDERS) 1 
By J. W. Abalos 
Institute) Nacional de Microbiologia, 
Santiago del Estero, Argentina 
The genus Latrodectus comprises a few species very hard to classify. 
The geographical distribution of some spreads across several contin- 
ents, 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 
( J 959) 2 use d for species identification, among other devices, the male 
genitalia as well as the female; thanks to this the problem of system- 
atics 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. geometricus 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. i in order not to add further confusion of names, 
resembles L. curacaviensis (Muller) 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 
Research under the sponsorship of Consejo Nacional de Investigaciones 
Cientificas y Tecnicas of Argentina. 
2 Levi, H. W. 1959. The spider genus Latrodectus (Araneae, Theridiidae) 
Trans. Amer. Micros. Soc., 78(1) :7-43. 
Manuscript received by the editor October 31, 1962. 
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