1968] 
Leuthold — Crematogaster 
345 
NO. OF 
ANTS/MIN 
30 
66 min 
a (ANTS REMOVED FROM BRIDGE) 
b (ANTS NOT REMOVED FROM BRIDGE) 
Fig. 8. Influence of the attractive effect of gathering ants on a foodless 
side bridge with trail. The passages onto the bridge were counted in 2 min 
periods. The significance of the difference between phase “a” and “b” is 
5% > p > 1% (Student’s test). 
effect of ants gathered at the joint (Fig. 8). Sometimes groups of 
two or three ants went together onto the side bridge. Tandem run- 
ning has been observed to be an important factor speeding the estab- 
lishment of mass-foraging. A forager ant, while turning back to the 
food, was often closely followed by a newcomer who was promptly 
led to the food. The influence of properties such as tandem running, 
active facing of encountered individuals and attraction to the crowd 
gains even more importance for the mass-recruitment during the 
stage in which a more or less continuous stream of ants starts flowing 
between nest and food. While this traffic builds to and from the 
food bridge, an increased rate of new ants follow the stream towards 
the side bridge rather than the old direction (Fig. 9). By consider- 
ing all possible components involved in the recruitment, the causes 
of an exponential rise to mass-foraging can be analyzed step by step. 
A description of the rise of mass-foraging is presented below. 
The first few explorer ants find the new food area independently 
by chance according to the basic probability of deviation from the 
main pathway. They are usually attracted to the food by the smell 
for the last few centimeters. After feeding or only touching or 
smelling the food, and often after a small orientation trip around the 
food, the first food finder turns back laying a trail. The trail is most 
efficient, as already mentioned, near the food, at the connection join- 
ing the food bridge to the old main bridge and on the turn merging 
into the old road. This first trace of a new scent trail alone some- 
what increases the deviation rate of bypassers. The food finder on 
the old pathways also presents an alerting signal to encountered ants. 
Such signals transmitted in the closest vicinity of the side turn in- 
crease once more the probability that stimulated ants will scout onto 
the new bridge (Fig. 3). Even though the new trail is weak and 
fragmentary, a relatively increased number of newcomers arrive on 
the base of the food bridge, and find the way to the food. The alert- 
