1988] O'Neill — Trail patterns of Formica obscuripes 3 
sum of the abdomen with dots of colored enamel paint; 2) a larger 
sample of unknown size was marked by spraying the surface of 
active nests with a fine mist of enamel paint, applying minute spots 
of paint to the surface of the ants. Workers ants marked in this 
manner continued to work on the nest surface and forage for the 
remainder of the season. This indicates that this marking technique 
did not have an adverse effect upon most workers. At least three of 
these workers were still present on nests on 15 March, 1987. Ants 
from nine nests were marked using these methods, allowing me to 
later determine the distance that many of the ants moved from the 
original location at which they were observed. 
Nest census techniques were modified from those of Scherba 
(1964). After tapping the surface of the nest to arouse the workers, 
all marked workers appearing over the next two minutes were 
counted, removed, and killed. This was done once each day on nine 
days between 25 August and 1 1 September. The study was termi- 
nated at this time because the railroad company had the tracks 
removed on 14 September. This destroyed many of the nests and 
disrupted much of the system of trails between the remaining nests. 
Censuses were conducted only before 1000 hours or after 1700 
hours, since workers did not remain on the nest in the middle of the 
day when surface temperatures were high (O’Neill and Kemp, 
unpublished). In the results, a single “crossover” refers to the recap- 
ture, on a censused nest, of one or more workers originally marked 
on another nest. Thus, if five workers marked on nest #6 were later 
recaptured on nest #1 1, this is recorded as a single crossover. 
To determine whether workers on a nest would tolerate the pres- 
ence of workers from other nests, an experiment was conducted in 
which workers were transferred between nests. The experimental 
group consisted of 40 workers collected on the surface of nests and 
transferred individually to other nests, not connected via a trail to 
the nest on which they were captured. As a control, 30 workers were 
moved between nests connected to one another via a trail system. A 
second control consisted of 5 workers removed from the surface of a 
nest and returned to the surface of the same nest. Each ant was 
handled only with a pair of forceps that had just been washed with 
ethylene chloride and air dried. After introduction to the surface of 
the nest, the worker was monitored until ten workers from the nests 
had made contact with it; during this period I recorded whether or 
not it was attacked by workers present on the nest surface. 
