BIOCHEMICAL DIFFERENTIATION OF THE 
SIBLING BLACK WIDOW SPIDERS, 
LATRODECTUS MACTANS AND L. VARIOLUS* 
By John D. McCrone 
Department of Zoology, University of Florida 
A recent revision of the black widow genus Latrodectus published 
by Levi (1959) has stimulated a great deal of interest in this medi- 
cally important group of spiders and has served as the basis for 
several subsequent investigations in various parts of the world 
(Abalos, 1962; McCrone and Levi, 1964; Szlep, 1965; Levi, 1966). 
All of these have shown that several species which are virtually in- 
distinguishable morphologically can readily be separated on the basis 
of various aspects of their biology. These findings in turn have led 
students of the group to seek additional taxonomic characters for use 
in the separation of these species. 
Rabaey and Verriest (1958) after a survey of the comparative 
agar gel microelectrophoretic patterns of the hemolymphs of 33 species 
of spiders, exclusive of any Latrodectus species, concluded such pat- 
terns could be very useful for the differentiation of species, par- 
ticularly those within the same genus. Encouraged by their results, 
I decided to determine whether a technique of this type would 
provide useful taxonomic information in the genus Latrodectus. 
This investigation was supported by Public Health Service Re- 
search Grant GM 11206 from the National Institute of General 
Medical Sciences. I wish to thank Miss Marietta Marra and Mr. 
Paul Dell for their technical assistance. 
Materials and Methods 
An increasing number of electrophoretic techniques have become 
available in recent years including agar, starch, disc and vertical 
acrylamide gel electrophoresis. All of the latter have been used to 
some extent in evolutionary and taxonomic studies (Manwell and 
Baker, 1963; Hubby, 1963; Hubby and Throckmorton, 1965; 
Coates, 1967) and have given satisfactory results. I have found, as 
did Hubby (1965), that the vertical acrylamide gel technique gives 
particularly good results. The acrylamide gel slab is much easier to 
handle than the starch gel and there is comparable resolution. Disc 
* Manuscript received by the editor May 15, 1967 
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