A NEW SPECIES OF WIDOW SPIDER 
(GENUS LATRODECTUS ) 
FROM SOUTHERN AFRICA 
(ARANEAE: THERIDIIDAE) . 
By Ian R. Mackay 
Harvard College, Cambridge, Mass.* 
Introduction. Despite numerous names there are apparently 
only a few species of widow spiders (Levi 1959). The members of 
the genus Latrodectus are of considerable interest since their venom 
has a fraction specific to vertebrates, as well as a group of proteins 
specific to insects, their normal prey. Several new species have re- 
cently been discerned as a result of studying the habits of sympatric 
black widows (Levi 1966, McCrone & Levi 1964). Minor but con- 
sistent differences in the genitalia were found later. Also, Abalos 
(1962,) found four sympatric species of black widows in Argentina, 
with different habits and egg-sacs. 
In this paper a new species is described from Rhodesia,; the first 
sibling species of the cosmopolitan Brown widow (L. geometricus) . 
This new species was first separated by the distinctive, smooth egg- 
sacs (Fig. 9). The two species seem to occur together. The geni- 
talia are distinct, in contrast to the sympatric L. revivensis, L. palli- 
dus and L. mactans tredecimguttatus in Israel (Levi 1966). 
I have not been able to match this new species to any of the pre- 
vious descriptions from Africa, most of which are based on color 
variations of L. geometricus. 
Egg-sacs The different egg-sacs (Fig. 9) first made me aware 
of the possibility of another species confused with L. geometricus. 
The egg-sacs of L. rhodesiensis are smooth, spherical and dirty white 
in color (pure white when first constructed). They are larger than 
the yellow, tufted cocoons of geometricus , with an external diameter 
of 10-18 mm (5-9 mm in egg-sacs of geometricus from Rhodesia). 
These smooth cocoons consist of an inner, pear-shaped, thin- walled 
sac — approximately half the diameter of the complete structure — 
surrounded by a layer of fluffy threads. 
Hemolymph In a search for other distinguishing characters I 
examined the hemolymph of the two species using electrophoresis, 
since McCrone ( 1967) separated sibling species of L. mactans by this 
*Mail address: Museum of Comparative Zoology, Harvard College, 
Cambridge, Mass. 02138. 
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