SPECIES OF WIDOW SPIDERS IN 
NORTHERN ARGENTINA 
( LA TR ODE CTUS : THERIDIIDAE) 
By L. J. Pinter 
Harvard University 
INTRODUCTION 
For more than fifty years there has been considerable controversy 
over the number of South American species in the genus Latrodectus. 
In a recent study Gerschman de Pikelin and Schiapelli (1965) re- 
ported that Latrodectus is represented by only two species, L. geo- 
metricus (Fabricius) and L. mactans C. L. Koch in Argentina. They 
opposed the findings of Abalos (1962), who suggested that at least 
five species of Latrodectus occur in Santiago del Estero, a northern 
province of Argentina. In addition to L. geometricus , Abalos proposed 
that four distinct species, temporarily designated No. 1, No. 2, No. 3 
and No. 4, comprise the mactans complex; whereas, Gerschman de 
Pikelin and Schiapelli believe that these four species . . . cannot 
be maintained because they are based only in the small differences 
in the form and size of their egg-sacs”. Abalos and Baez (1967) 
supported the original findings of Abalos with additional ecological 
and morphological data. The present paper is concerned only with the 
four sympatric populations placed by Abalos and Baez into the 
“ Latrodectus curacaviensis group” (No. 1) and the “ Latrodectus 
mactans group” (Nos. 2, 3 and 4). 
I would like to acknowledge with sincere thanks the constant ad- 
vice and encouragement by Dr. H. W. Levi of the Museum of 
Comparative Zoology and the loan of material by Dr. J. W. Abalos 
of the University of Cordoba, Cordoba, Argentina. The study was 
supported in part by Harvard University and by Public Health Serv- 
ice Research Grant AI-01944 from the National Institute of Allergy 
and Infectious Diseases. 
METHODS 
In suggesting that the (( curacaviensis-mactans ,, complex was com- 
prised of four species, Abalos relied heavily upon field observations 
made in Santiago del Estero. On the other hand, Gerschman de 
Pikelin and Schiapelli relied mainly upon their studies of the mor- 
phological variations of specimens collected throughout Argentina 
and at least two neighboring countries. In order to minimize the 
problem of geographical variation within species, I limited my study 
to specimens collected in the small region sudied by Abalos. Further- 
more, the study specimens were recently captured adult females which 
