1981] Holldobler — Communication in Orectognathus 
253 
glands. All ants following the trails to the end during a 5-minute 
period were counted. 
As can be seen from table 1, trails drawn either with crushed 
pygidial glands or poison glands elicited a precise trail following 
behavior in all three worker castes (Fig. 6), but the ants did not 
respond to trails drawn with crushed Dufour’s glands. We noticed, 
however, several differences in the reaction of the ants to poison 
gland trails and pygidial gland trails. (1) When both trails were 
offered simultaneously, starting at the periphery of a “homeless” 
colony, significantly more workers (Tab. 1) carrying brood moved 
along the poison gland trail. (2) In all tests the poison gland trail was 
the more effective one and lasted over a longer period of time. After 
5 minutes the ants’ response to pygidial gland trails had almost 
vanished, whereas they were still strongly following the trail drawn 
with poison gland material. In fact, poison gland trails presented to 
the ants 24 hours after they were drawn were still effective as 
orientation cues for emigrating O. versicolor workers. (3) Although 
we could not detect a preference for either trails drawn with poison 
glands or pygidial glands, ants moving along the pygidial gland trail 
seemed to gape their mandibles more frequently than ants moving 
along poison gland trails. 
From these observations we conclude that the trail pheromones 
serve different functions. The poison gland trail is obviously 
employed during nest emigrations, where it serves as a stimulative 
recruitment signal as well as a longer lasting orientation cue. On the 
other hand, the pygidial gland trail probably functions as a relatively 
short lasting alarm-recruitment signal, channeling workers to areas 
of disturbance near the nest. It is also possible that the pygidial 
gland pheromone is discharged by successful foragers when they 
return to the nest, which might cause the social facilitation of the 
foraging activity mentioned above. In fact, when a crushed pygidial 
gland is presented inside the nest tube, it elicits more excitement in 
the workers than any other glandular secretions (mandibular gland, 
poison gland, Dufour’s gland), causing several workers to move 
toward the nest entrance. 
All three worker castes have the same glandular equipment and 
their secretions release the same behavioral responses. 
