1961] 
Blum, Roberts , and Novak — Solenopsis 
74 
spectra represent are very similar. On the other hand, whereas the 
venom of S. saevissima contains two rhodamine-complexing minor 
components, the venom of S. xyloni contains only one. 
The chemical similarities of the two venoms are paralled by their 
biological properties. The venomous principles of S. xyloni exhibit 
the same antimycotic and antibacterial activities as are found in the 
venom of S. saevissima (Blum et al. 1958). The pronounced hemolytic 
effect and insecticidal activity of S. xyloni venom compare to these 
same properties in the venom of S. saevissima (Adrouny et al. 1959; 
Blum et al. 1958). Thus the venoms of both of these fire ants feature 
the same broad-spectrum activity against diverse types of cells. 
The skin responses of human beings to the stings of these two fire 
ants are similar only during the first few hours, both being charac- 
terized by an immediate flare followed by a wheal. However, whereas 
the sting of S. saevissima is always characterized by an umbilicated 
pustule at the sting site (Caro et al. 1957), we have found that the 
response to the sting of S. xyloni seldom results in more than a mild 
prurience. In the few cases where minute pustules were observed, 
they were on individuals who were quite sensitive to the sting of 
S. saevissima. At least three explanations seem possible : ( 1 ) minor 
structural modifications of the necrotoxin in the venom of S. saevissima 
are associated with a large increase in necrotoxicity when compared to 
its counterpart in the venom of S. xyloni (2) the concentration of 
the necrotoxin in the venom of S. saevissima is greater than its counter- 
part in the venom of S. xyloni, (3) the minor components contribute 
to the necrotoxic action of the venom. These hypotheses remain to 
be determined experimentally. 
References Cited 
Adrouny, G. A., V. J. Derbes, and R. C. Jung. 
1959. Isolation of a hemolytic component of fire ant venom. Science 
130:449. 
Blum, M. S. and P. S. Callahan. 
1960. Chemical and biological properties of the venom of the imported 
fire ant ( Solenopsis saevissima var. richteri Forel ) and the isola- 
tion of the insecticidal component. XI Int. Kongr. Ent., Vienna. 
3:290-293. 
Blum, M. S., J. R. Walker, P. S. Callahan, and A. F. Novak. 
1958. Chemical, insecticidal and antibiotic properties of fire ant venom. 
Science 128:306-307. 
Caro, M. R., V. J. Derbes, and R. Jung. 
1957. Skin responses to the sting of the imported fire ant ( Solenopsis 
saevissima ) . A. M. A. Arch. Dermotol. 75:475-488. 
