1988] 
O'Neill — Trail patterns of Formica obscuripes 
9 
Table 3. Results of introduction of worker ants to the surface of nests. Each was 
handled only with a pair of clean forceps and was watched for 30 s after being in 
introduced. 
Manipulation 
# ants 
tolerated 
# ants 
attacked 
Total 
% Attacked 
Moved from site 15 km away 
to nests of group A 
0 
10 
10 
100 
Moved from site 1 km away 
to nests of group A 
0 
10 
10 
100 
Moved between nests of 
group A and group D 
4 
16 
20 
80 
Within nest group switches: 
group A 
20 
0 
20 
0 
Within nest group switches: 
group D 
10 
0 
10 
0 
Sham switches (ant picked 
up and returned to 
same nest) 
5 
0 
5 
0 
both within and between nest groups. The vast majority of workers 
found to move to other nests were recaptured within the same nest 
group: 99% of workers from group A that were recaptured and 77% 
of workers from group C that were recaptured. This occurred even 
though the absolute distance between nest groups was often much 
less than the distance between given nest pairs that exchanged 
workers within a group. For example, while the distance moved by 
workers within group A was often greater than 50 meters, they were 
rarely found to leave the nest group and join nests of other groups 
that were sometimes just several meters away from the trail system. 
Within nest groups, a mound did not always receive the same 
number of marked workers that were found to move from it to other 
nests. Furthermore, marked workers moving off of a nest did not 
distribute themselves evenly among other nests within a nest group. 
As indicated by occasional recapture of marked ants on nests out- 
side of their “home” nest group (Table 1) and the results of experi- 
ments transferring workers between nests in groups A and D (Table 
3, row 3), the barrier between nest groups was not absolute. This 
suggests, perhaps, that territoriality in these ants is expressed as a 
graded effect, with tolerance for conspecifics from other colonies 
decreasing with distance or the duration of time passed since two 
