1988] 
O'Neill — Trail patterns of Formica obscuripes 
7 
Table 1. The number of different crossovers (i.e. where at least one marked 
individual from a nest was found on censused nest) and the number of marked 
workers observed during censuses. All workers were originally marked on one of 
eight nests in group A. Comparison on different crossovers within group A to those 
from group A to other censused nests (i.e. row 5 vs. row 6), Xi = 36.0, P < 0.001. 
Censused Nest 
Group (# nests) 
Different Crossovers 
tt Workers 
Crossing Over 
Observed 
Possible 
% 
Observed 
Mean #/ 
Nest 
Group B ( 1) 
1 
8 
12.5 
1 
1.0 
Group C (3) 
0 
24 
0 
0 
0 
Group D (2) 
0 
16 
0 
0 
0 
Others not in 
Groups (3) 
1 
24 
4.2 
2 
0.7 
SUBTOTAL 
(Non-Group A) (9) 
2 
72 
2.8 
3 
0.3 
Group A (20) 
86 
152 
56.6 
402 
20.1 
Overall Total 
88 
224 
39.3 
405 
14.0 
these, 152 (49%) were found on nests other than those on which they 
were marked (Table 2). 
Lack of tolerance of ants from one nest group for ants of another 
was demonstrated in experiments in which ants were transferred 
between nests. Ants taken from distant nests and placed on nests in 
group A were always vigorously attacked by workers on the surface 
of nests (rows 1 and 2 of Table 3). Attacking ants attempted to bite 
and seize the intruder with their mandibles and often succeeded in 
dragging the intruder into the nest. This was essentially the same 
type of aggressive response to alien workers reported for Formica 
fusca (Wallis, 1962). Intruders were sometimes attacked within sev- 
eral seconds, with as many as six attackers eventually surrounding 
them. A similar result was found when ants from groups A and C 
were switched between groups (row 3). On the other hand, ants in 
control manipulations were not attacked (rows 4-6). 
Observations on a section of the trail near nest #6 (Figure 1) 
showed that ants marked on other nests in the same nest group (A) 
brought dead arthropods and honeydew to this nest. In 51 ten min- 
ute censuses on 14 days between 21 July and 20 August, 52 marked 
ants were carrying liquid (probably honeydew) to the nest (i.e. they 
had extremely distended abdomens and regurgitated liquid when 
