6 
Psyche 
[March 
Since workers of the different attine genera follow each others’ arti- 
ficial trails in the laboratory, the question arises as to whether this oc- 
curs in the field. The tribe Attini is limited to the New World where 
most of the genera are sympatric. Weber (1958) has emphasized the 
fact that the attines are tolerant of one another as indicated by the 
fact that different genera forage beside one another, without any 
hostility. Furthermore, Weber notes that nests of genera such as 
Gyphomyrmex and Trachymyrmex are commonly found in the soil of 
the Atta mounds. These facts certainly emphasize the probability that 
under field conditions, the odor trails of different attine genera can 
frequently overlap. Indeed, strong trails of Atta cephalotes and 
Acromyrmex octospinosus crossed in at least two different places in a 
field that we observed at Alajuela, Costa Rica. In no instance were 
workers of either species observed to violate the other species’ trail. 
When Acromyrmex workers were placed on the Atta trail, they in- 
variably wandered off the trail almost at once and resumed trail fol- 
lowing on their own trail when it was encountered. It does not seem 
unlikely that the persistent trails which attines follow over long 
periods contain secretions other than their odor trail substances which 
may render them more specific. Likely sources of trail additives are 
anal emissions which should present a considerable accumulation on 
a trail which is being utilized for extended periods. It is interesting 
to note that the odor trail of the formicine Lasius fulginosus (Lat- 
reille) is derived from an anal emission (Carthy, 1951). Whether 
attine odor trails maintain their specific identities among the tribal 
members because of supplemental secretions remains to be proven. 
However, in view of the non-specificity of the demonstrated odor 
trail substances among the Attini, it seems necessary to propose that 
additional chemical stimuli are present on the trails. 
Nothing is known about the chemical nature of the attine odor 
trail substances. Preliminary examinations of the contents of the 
poison vesicles of the four attine genera indicate that all the secretions 
have similar physical properties. The vesicle contents are viscous, 
water-clear liquids which produce a strongly alkaline reaction with 
various indicator papers. When the poison vesicle is ruptured, its 
liquid contents immediately are converted into a semisolid mass. This 
latter property of the poison gland contents is certainly consistent 
with what is known about the general nature of the attine odor trail 
substances especially among the more highly developed genera. The 
persistent trails of Atta certainly reflect the presence of an odor trail 
substance (s) with a low vapor pressure. Assuming that the sting 
secreted odor trail substance similarly solidifies under field conditions, 
