The document describes an experiment investigating whether pheromones left by Red Harvester Ants help guide other ants to food sources more quickly. The experiment found that the first "patroller" ant took the longest on average to find food, while subsequent ants grew quicker at finding food. This suggests the patroller ant leaves a scent trail that helps later ants locate food faster. The study supports the idea that pheromones play a role in the foraging efficiency of Red Harvester Ant colonies.

1. Haley Hodoval
BIOL 1108L
Bryanna Libby
7 November 2013
The Role of Pheromones and Aiding Red Harvester Ants when Searching for Food
Introduction:
Pogonomyrmex barbatus, more commonly known as Red Harvester Ants, were
the subject of our experiment about studying pheromones. When it comes to discovering
food for their colony, the forager and the patroller are the two most important roles to
help find food for their fellow ants. The patroller is the initial ant that leaves the colony to
go out and discovers where the food is for the colony. The forager follows up the
patroller after they have returned to the colony. The forager then leaves the colony and
follows the trail the patroller left behind them in order to discover the food the patroller
ant initially found. The forager will then return to the colony with the food it has
discovered (Gordon 2002). The main way the Red Harvester Ants communicate is by
touching each other’s antennae. Chemical signals are transferred and their encounter can
result in a change in behavior (Gordon 1999).
We came across an experiment that was designed to determine if there is a
connection between an increase in foraging activity and whether or not pheromones play
a role in Red Harvester Ants foraging activity. They tested whether or not the foraging
Red Harvester Ants that initially left the nest, “respond[ed] to the odor of food, oleic acid,

2. the odor of the forager itself, cuticular hydrocarbons, or a combination of both with
increased foraging activity” (Green, et.al 2013). Their results showed that there was an
increase of foraging acitivity when P. barbatus returned when the odor left behind from
the food, like oleic acid, and their own scent they left behind. When the Red Harvester
Ants with a combination of odors from food as well as the ones they left behind returned
from their foraging activity and interacted with the other ants, there was an strong
increase in foraging activity as opposed to those that returned with just one or the other
(Greene, et. al 2013). Our goal was to discover whether or not Red Harvester Ants use
the pheromones from a previous ant’s excursion to aid them in finding food.
Materials and Methods:
We wanted to know the process of how ants sustain life in their colony through
foraging for food so we designed an experiment that studies the foraging habits of Red
Harvester Ants. We used choices chambers with sugar placed into two quadrants of each
chamber. For the first round, we placed sugar in adjacent chambers and timed one
individual ant to see how long it took the ant to find the sugar. When the ant stopped over
the sugar for 2-3 seconds, we considered that as the ant finding the sugar. Then we
proceeded to add another ant and time it as well until it found the sugar. We continually
added ants one after the other, while leaving the previous ones in there. We stopped
adding ants at a max of five. We completed this round, where the sugar was placed in the
adjacent chambers, using three trials with 5 each being used in each trial. For each trial a
separate choice chamber was used to avoid having the new ants follow the pheromones of
its predecessors.

3. We recorded all of out data, specifically the amount of time it took each to find
the sugar, and observed how the ants went about finding the sugar. The second round we
placed the sugar in side by side chambers for each choice chamber. The same method
was used with a total of 5 ants being used in each trial. We placed the food in adjacent
chambers for one and side-by-side chambers for the other to see if the ants had a
preference for either and to see if they found it quicker in one over the other. Also, we
wanted to make sure that they didn’t favor one direction over the other so we wanted to
account for all variables by using two different placements for the sugar.
Results:
After recording the time for each individual ant, our data showed that the first ant
placed into each choice chamber was generally the slowest ant to find food. The only
exception was if the second ant that followed found the other choice chamber. After at
least one ant found sugar, the majority of the times that followed were less than the first
ant that found food in the chamber, also known as the patroller. We noticed that
sometimes when we would add a new ant, it would stop right next to an ant that had been
placed in there previously. They looked like they were touching each other, as if they
were communicating to one another. Often times, after this communication, the most
recently added ant would then find the food within the next 30 seconds or so.

4. Figure 1: The average amount of time it took each individual ant to find food in their
respective choice chamber.
Discussion:
We believe the large time difference between the first ant that found a chamber
with sugar and the ants that followed him, were because of the pheromones that the first
ant that found that chamber of sugar left behind as a guide to the food. Yes, sometimes
the second ant took longer to find food than the first, however that ant generally found
the sugar that was in the other chamber that the first ant didn’t find. The ants that
followed them always found the sugar, sometimes both chambers, in a less amount of
time than its predecessors. We have determined that the pheromones are what guide the
ant to the food, thus making it easier and quicker for the rest of the ants in their respective
colonies to have access to the food.
The frequent communication we saw between the two ants supports the theory
that they communicate and how that can change their behavior. We also noted that our
results are similar to that of Greene’s experiment. Although we can’t measure the
foraging activity of an entire colony, we can observe the sample of ants we used in our
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Ant
Average Time for Ant to Discover
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Trial 2 Averages
Trial 1 Averages

5. experiment. It’s difficult to tell whether or not the scent of the food contributed to a
decrease in foraging time for ants that followed the initial patroller ants. However, we can
back up the claim that when the initial patroller ant goes out in search of food, there is a
decrease in the amount of time it takes the following ants to discover the food. Ultimately
we believe this is due to the pheromones the patroller ant leaves behind, just like the
patroller ant in Green’s study.
Citations:
Greene, M.J., Pinter-Wollman, N., and Gordon, D.M., 2013. Interactions with combined
chemical cues inform harvester ant foragers' decisions to leave the nest in
search of food, PLOS ONE. Vol. 8 (1): 1-8.
Gordon, D.M., Chu, J., Lillie, A., Tissot, M., and Pinter, N., 2005. Variation in the
transition from inside to outside work in the red harvester ant pogonomyrmex
barbatus, Insectus Sociaux. Vol. 52 (3): 212-217.
Gordon, D.M. 2002. The regulation of foraging activity in red harvester ant colonies,
American Naturalist. Vol. 159 (5): 509-519.
Gordon, D.M., and Mehdiabadi, N.J., 1999. Encounter rate and task allocation in
harvester ants, Behavioral Ecology & Sociobiology. Vol. 45 (5): 370-377.
Ingram, K.K., Oefner, P., and Gordon, D.M., 2005. Task-specific expression of the
foraging gene in harvester ants, Molecular Ecology. Vol. 14 (3): 813-8.

6. Wehner, R., Meier, C., Zollikofer, C., 2004. The ontogeny of foragwehaviour in desert
ants, Cataglyphis bicolor, Ecological Entomology. Vol. 29 (2): 240-250.
Abstract: We wanted to discover if there was a connection between the pheromones Red
Harvester Ants leave behind when patrolling for food and whether or not that helps
contribute to future ants finding food in a more timely manner. We designed an
experiment using choice chambers where we placed food into two different chambers and
timed the ants that we consecutively placed into that chamber. We recorded the time of
each individual ant and because of the average drop in foraging time for each ant
following the first patroller ant, we determined that pheromones left behind from the
patroller ant aid its successors in discovering food quicker.