POSTEMBRYOLOGICAL DEVELOPMENT OF 
SPIDERLINGS FROM TWO PERUVIAN 
LATRODECTUS POPULATIONS 
By John D. McCrone, Florida Presbyterian College 
AND 
Herbert W. Levi, Harvard University 
It is becoming increasingly clear that the solution of the complex 
taxonomic problems presented by the black widow genus Latrodectus 
will require more basic biological data than are now available. Of 
particular importance in this regard is information on the postembryo- 
logical development of color pattern. Many Latrodectus populations 
show marked interpopulation differences in color pattern particularly 
of the immature stages. It is difficult to assess the taxonomic sig- 
nificance of these differences without reliable information on the de- 
velopment of these patterns in various populations. 
Little such information has been published. The most extensive 
study was that done by Smithers (1944) with Latrodectus mactans 
indistinctus . He raised spiderlings from three different areas in 
South Africa and recorded the rate of development and the changes 
in color pattern after each molt. Unfortunately he confined his ob- 
servations on color pattern to the females. 
Recently we were able to obtain egg sacs from two different 
areas in Peru, Lima and Cuzco. We have reared 54 adults from 
these sacs and have recorded the changes in their color pattern 
after each molt. Morphologically these adults all appear to be 
Latrodectus mactans , probably the same as Latrodectus species “no. 
3” of Abalos’ cultures from Santiago del Estero Province in Argen- 
tina. 
The spiders were raised in the laboratory in St. Petersburg, 
using a technique previously described (McCrone and Levi, 1964). 
A record was kept for each developing spider of the number of molts 
to maturity, the duration of the stadia, and the color pattern of each 
post-emergent instar. These data are presented in Table 1 and Figs. 
1 -1 9. The color patterns figured are the basic patterns found in 
each population. There were slight individual differences in pattern; 
however^ these did not obscure the basic color patterns. 
From the illustrations it can be seen that some instars are more 
polymorphic than others (Fig. 2, 15, 16) even though the adults 
end up with more or less similar patterns in females (Fig. 9, 18, 19), 
* Manuscript received by the editor June 28, 1966. 
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