1981] Holldobler — Communication in Orectognathus 
247 
nor did it appear that workers leaving the nest followed chemical 
trails. 
On the other hand, trail following was very obvious when the 
colony or fragments of the colony were forced to move to a new nest 
site. For example, when we shook the colony out of the nest tube 
into the arena, which had been provided with a new papered floor 
before each experiment, the “homeless” colony soon gathered at one 
spot, where it was closely guarded by members of the major worker 
caste (Fig. 1). After varying intervals (sometimes lasting more than 
one hour), some of the minors and medias began exploring the 
arena, and eventually they discovered a nest tube that had been 
provided at the edge of the arena (usually 30-35 cm away from the 
displaced colony). After exploring the nest tube, some of the ants 
returned to the colony, and after a while they often moved again to 
the nest tube to continue to explore it thoroughly. 
Usually this procedure was repeated several times, before the first 
signs of a colony movement could be observed. It occurred when 
several additional minors and medias departed from the colony and 
traveled directly to the new nest. Their straight orientation and the 
fact that during running they kept the tips of their antennae close to 
the ground, suggested that these ants were following a chemical 
trail. Soon afterwards the traffic between the “homeless” colony and 
the newly discovered nest tube increased leading finally to a full- 
scale colony emigration. 
All three worker castes were involved in transporting brood, 
callow workers, and males to the new nest, although the minors 
handled eggs and small larvae preferentially while the medias and 
majors concentrated on large larvae, pupae and adults (Fig. 2). 
Usually the queen moved during the early phase of the colony 
movement and always traveled on her own. On the other hand, the 
males were always carried by the workers (Fig. 2), usually not before 
most of the brood had already been moved. Only once did we see a 
fully pigmented worker being carried by a nestmate. The trans- 
ported individual was grasped dorsally at the head and lifted 
upwards with gaster tip pointing forwards; it had the appendaes 
folded in the pupal position. All ants traveled along a relatively 
narrow route between colony and new nest site. This strongly 
suggested that O. versicolor employs chemical trail communication 
during the process of colony migration. The following experiments 
