338 
Psyche 
[December 
5 cm 
Fig. 3. Ant walking over a star-shaped bridge encounters food finder 
(heavy arrow), receives the alerting stimulus and responds by the zigzag 
run into areas adjoining the trail, with occasional loops and circling, raising 
of the gaster is typical (dotted line). (Other crossing ants contacted are 
marked by*. Diagram from a movie film, 16 frames per second). 
release of recruitment behavior. The recruitment begins with the 
first trail-laying on the return way from the food. The ant moves 
slowly, shuffling its hind feet against the substrate and releasing the 
trail pheromone from the hind tarsi (Leuthold 1968, Fletcher and 
Brand 1968). The most intensive trail-laying is performed just 
after leaving the food place, at the connecting joint between the two 
bridges and at the turn which merges into the old pathway. Between 
these places trail-laying often fades partially, so that this first trail 
arises discontinuously. If the trail is already well established, the 
food finder ant usually lays a weak trail or no trail at all on the old 
pathway. It rushes nestwards obviously activated and excited. When 
it encounters other workers on the trail it performs a new alerting 
behavior which is an individual recruiting signal. The food finder 
ant actively faces the encountered nestmate and standing more or 
less still it shaxes its head vigorously towards the other’s face. This 
fast vibration of about 12 strokes per second lasts from 1/6 second 
to 1 second ; then the two ants separate. More details of this alert- 
behavior are resolved by slow motion cinematography (Figs. 1 and 
2). The alerting ant flings its head from a slightly ducked, nearly 
opposite position towards the head of the encountered worker, usual- 
