THE ANATOMICAL SOURCE OF TRAIL SUBSTANCES 
IN FORMICINE ANTS 1 
By M. S. Blum 2 and E. O. Wilson 3 
Carthy (1951) showed that when workers of the formicine ant 
Lasius fuliginosus (Latreille) lay odor trails, they emit minute 
streaks of liquid that can be made visible to the naked eye by dusting 
with lycopodium power. By tracing food marked with edible char- 
coal, Carthy further proved that at least some of the liquid comes 
from the hind gut. He concluded that the trail substance is pro- 
duced by the hind gut, probably as a component of the ingested gut 
contents rather than as a special secretion of the gut walls. In fact, 
this conclusion does not necessarily follow from the experimental 
results. It is equally possible that the critical trail substance is pro- 
duced by another organ (e. g. the poison glands) and added to the 
anal streak. The necessity of considering such an alternative has 
been impelled by the discovery in recent years that the trail substances 
of certain non-formicine species are powerful attractants generated as 
glandular secretions in trace amounts (Wilson, 1963). 
Nevertheless, even though Carthy’s original evidence was not 
definitive, it now appears probable that his conclusion is basically 
correct. Using the artificial trail technique (Wilson, 1959), which 
allows a more certain identification of the anatomical source, we 
have been able to establish that in two other formicine species, 
Myrmelachista ramulorum Wheeler and Paratrechina longicornis 
(Latreille), the hind gut is the true primary source. Since no non- 
formicine ant species investigated thus far shares the character, the 
interesting possibility is raised that the hind-gut source is a unique 
evolutionary innovation of the Formicinae. 
Procedure and Results 
Myrmelachista ramulorum. The workers of this species form some 
of the longest and most conspicuous trail formations found in the 
Formicinae. At Mayaguez, Puerto Rico, where the species is abun- 
dant, it was noted that workers following trails frequently touched 
This work was supported in part by National Science Foundation Grants 
G22074, G19200 and a grant from the University Council on Research of 
Louisiana State University. 
department of Entomology, Louisiana State University, Baton Rouge, 
Louisiana. 
3 Biological Laboratories, Harvard University, Cambridge, Massachusetts. 
Manuscript received by the editor November 12, 1963. 
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