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Psyche 
[September 
and quite different ones in males (Fig. 5, 13). The adult male is 
lighter than in the previous instar and the adult female is darker 
than in the penultimate stage. The individual variation of adult males 
is greater than that of adult females. 
The spiderlings from Cuzco went through different color phases 
than did the Lima spiderlings although the adults are similar. Smith- 
ers (1944) reported the same phenomenon in South Africa. Adult 
females from the Little Karroo and Port Elizabeth were identical, 
but the color patterns of the immatures were quite different in the 
two groups. Considering the geographical proximity of the two 
Peruvian populations the differences in color pattern are remarkable. 
Males from the Peruvian population were mated with L. mactans 
mactans from Florida. Although they readily mated and egg sacs 
were produced, none of the eggs hatched. Unmated Latrodectus do 
not produce an egg sac at all. Similar results were obtained when 
female L. mactans tredecimguttatus from Israel were mated with 
Florida L. mactans. The significance of this reproductive isolation 
is unclear because we have made no crosses with geographically 
intermediate populations. Members of different sympatric Florida 
species can not be mated with each other in the laboratory. The same 
observation has been made in Argentina (Abalos, pers. comm.). 
The marked intra- and interpopulational differences in the color 
patterns of the immature and adult spiders from the two Peruvian 
populations studied show that the use of color pattern as a diagnostic 
species character must be done with great caution. For example, 
that some collections of juveniles from Texas were almost white, 
others black, seems to be of little significance. Both colorations 
were found after one molt (Fig. 2) from the same egg sac. Color 
pattern differences have significance only when they can be correlated 
with other morphological and biological characters (e.g. L. bishopi). 
Explanation of Plate 10 
Figures 1-9. Latrodectus mactans from Lima, Peru; coloration diagram- 
matic. Left venter, right dorsum with legs. Molts counted from after 
leaving egg-sac; there is one molt within egg-sac. 
Fig. 1. After hatching (males and females). Fig. 2. After first molt 
(males and females) ; at right, variant pattern of about 10%. Fig. 3. After 
second molt (males and females) ; at right, variant pattern. Fig. 4. After 
third molt (penultimate male). Fig. 5. After fourth molt (adult male). 
Fig. 6. After third molt (female). Fig. 7. After fourth molt (female). 
Fig. 8. After fifth molt (female). Fig. 9. After sixth molt (adult female). 
White: white; crosshatch: light brown; double crosshatch: dark brown; 
light stipple: orange; dark stipple: red; black: black. There may be a 
yellow fringe around the red in areas marked white. 
