26 
Psyche 
[March - June 
Atta. A faint “meaty” odor was noticed as I brought my face close 
to the column ; this odor increased markedly when I agitated a part 
of the column with my machete, and the ants savagely attacked the 
blade, biting and attempting to sting. (The meatlike odor of some 
New World army ants has been well known for years.) Selecting 
one of the large soldiers, with its conspicuous, shiny whitish head 
and long hooked jaws, I removed the head with forceps and placed 
it in the column, where it was at once vigorously attacked, bitten and 
stung by a mass of workers and soldiers that collected around it. 
The actively struggling body of this same soldier was then placed in 
the column at another point; the headless body, despite its consider- 
able and highly irregular activity, attracted only momentary antennal 
play from passing nestmates. 
Several more trials like this were made at different points along 
the column ; it was found that soldier heads attracted more attackers 
than did the much smaller worker heads tried, and also that freshly 
crushed soldier heads drew a stronger attack than intact ones. To my 
nose, the strength of the meaty odor in each case appeared to be 
roughly proportional to the number and activity of the attackers, and 
I could detect none of this odor from the postcephalic part of the 
body after the heads had been removed. (Later, in the laboratory, 
crushed soldier heads of E. hamatum were sniffed by two colleagues 
and myself, and compared directly with the odor of beef and vege- 
table bouillon cubes, with the result that all of us found the odors 
close if not identical.) 
Next, small dead twigs were broken in half, and one half rubbed 
against the crushed head of a worker. Such twigs when placed in the 
column were subjected to an attack as massive and vigorous as were 
the crushed heads alone. The untreated half of each twig, serving 
as a control placed at another point along the column, never re- 
ceived more than fleeting attention from passing soldiers and workers. 
Similar results were consistently obtained with another column of 
E . hamatum found on a subsequent day. 
The same kind of investigation was carried out briefly with a 
column of Nomamyrmex esenbecki (Westwood) found in the forest, 
utilizing the large and medium-sized workers for the decapitation 
test (this species lacks large soldiers). To my nose, crushed heads 
of this species have a different and weaker odor than do E. hajnatum 
workers of the same size, but the alarm and attack reaction they pro- 
voked was similar to that of hamatum in intensity. 
The test was also made with soldiers from a raiding swarm of 
