also recorded each minute. In all combinations, the first observation was made five
seconds after all ants were released into the Petri dish. At the end of the 5- or 1 O-minute
observation period, the ants were then left in the Petri dish for 1 or 2 hours, and a
mortality score was recorded after each hour. All statistical analyses were performed
using JMP 7.0.2 (SAS Institute Inc., 2007). Each of the aggression assays is explained in
ftɪrther detail below.
Crazy ants vs. small and large fire ants
Aggression assays between crazy ant workers and fire ant workers of different
sizes were conducted on July 16,2008. Each of 12 fire ant colonies was used twice as a
source of workers, the first time with 5 small workers paired up with 5 crazy ant workers,
and the second time with 5 large workers paired up 5 crazy ant workers from a different
colony, creating a total of 24 aggression trails. Aggression and fighting data were
recorded for 10 minutes. Mortality was recorded after 10 minutes, and for 10 pairings,
also after 1 hour.
In order to quantify the size difference between crazy ants and minor and major
fire ant workers, the head length (from the front of the clypeus to the posterior margin of
the head) of 10 ants from each of the 3 groups was measured. Head length is considered
the most reliable predictor of body size across ant species (Kaspari and Weiser 1999).
The average and standard error of the length was calculated for each group, and the head
lengths were tested for a significant effect of ant type using a one-way ANOVA,
followed by a post hoc Tukey’s test to discern between the 3 types. The head lengths of
each type of ant (crazy ant, small fire, and large fire ant) were all significantly different
from one another (Fa,29 = 262.87, p = <0.0001, Table 2.1). In order to estimate the size
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