1964] 
McCrone and Levi — Latrodectus 
25 
passed through to maturity. The first post-emergence molt was con- 
sidered the first molt. These data are summarized in Table I. 
A total of 45 L. mactans and 44 L. variolas reached maturity. The 
sex ratio for L. mactans was 19 males to 26 females, for L. variolus 
22 males to 22 females. A chi-square analysis at the 5% level of 
significance demonstrated that both these ratios are consistent with the 
hypothesis of a 1 :i sex ratio. 
Male L. mactans passed through fewer molts to maturity (mode 4) 
than male L. variolus (mode 7). Male L. mactans matured in an 
average of 42.0 ± 7.8 days (range 32-58) while male L . variolus 
took much longer, 129.6 ±7.5 days (range 122- 135). 
The same relationship held for the females. Latrodectus mactans 
females required from 5 to 8 molts (mode 6) to maturity, L. variolus 
females 7 or 8 molts (mode 7). Females of L. mactans averaged 63.8 
± 9.4 days (range 53-90) to maturity, while females of L. variolus 
averaged 152.6 db 17.9 days (range 125- 199). The discrepancy in 
number of instars suggests that the greater number of molts of L. 
variolus determines the very much larger size of the males, and also 
that the size variation and well-known variation in coloration of L. 
mactans males might be due to the different number of molts under- 
gone. 
Species Relationships 
Latrodectus bishopi and L. variolus are certainly distinct species, 
but the close similarity between the two in morphology and their al- 
lopatric distribution suggests that L. bishopi might have been derived 
from L. variolus. It is known that the sand-pine scrubs inhabited by 
L. bishopi arose in connection with islands that were present in the 
Florida area during the Pleistocene (Laessle, 1958). The literature 
(see Neill, 1957) records a number of species that are endemic to 
these scrubs or other south-central habitats in Florida. Many of these 
species are closely related to other species whose ranges extend only 
into northern Florida. Thus the conjecture can be made that L. 
bishopi differentiated from L. variolus on an isolated island or island 
group in the Pleistocene seas. 
Explanation of Plate 4 
Figs. 23-25. Habitat of L. b'shopi. 23. Florida scrub pine. 24. Web in 
palmetto. 25. Close-up of female with egg sac in palmetto. 
Fig. 26. Latrodectus mactans (Fabricius) female from Tennessee. 
Fig. 27. Latrodectus variolus Walckenaer. female from northern Florida. 
(Photograph by H. K. Wallace) 
Fig. 28. Habitat of L. variolus in lower limbs of trees in northwestern 
Florida. 
