The Effects of Sun on the Activity of Cone Ants

by Rebecca Carty and Brooke Mayo

Science Ed 506

OssabawIsland Experiment

May 29, 2004

ABSTRACT

The purpose of our study was to learn more about the activity of Cone Ants, Dorymyrmex bureni. We were interested in seeing if sunlight affected the activities of ants. To investigate this, we collected data on the activity of ants at eight anthills, located on OssabawIsland in conditions ranging from full sunlight to full shade. Our observations revealed a negative correlation between the amount of sunlight and the number of active ants at each anthill. As the amount of direct sunlight increased, the activity of ants decreased.

INTRODUCTION

Initial observations suggested that the ants at some anthills were more active than at others. We considered several questions to assist us in our investigations. Initially, we wanted to see if there was a difference in ant activity based on the location of the anthill. We began our experiment by choosing anthill sites in a forested area and a dune area. As we collected data, we became more interested in the effects of sunlight, rather than in differences in location.

Upon researching ant behavior, we found that ants normally live underground in the dark; they can be upset by bright light. However, black ants will often work in daylight, while other species prefer shaded areas (Taz 2004). Ants respond to sunlight in various ways. For example, when Red Ants are exposed to sunlight, they typically show aggressive behaviors (CDFA 2004).

GUIDING QUESTIONS

First, does the amount of direct sunlight on an anthill affect the activity of Cone Ants? We suspected that there would be less activity on anthills with direct sunlight due to the high temperature of the sand. Second, is there a difference in ant activity between anthills where sunlight is less due to the presence of canopy, compared to anthills that are located in more open areas? We believed that sites with canopy would have more shade and the open areas would have more direct sunlight. Third, does the size of the anthill correlate to ant activity? We suspected that larger anthills might contain more ants, which could translate into a larger number of ants actively engaged in foraging.

METHODS

Four active anthills in the forested area and four active anthills in the dune area adjacent to the OssabawIsland campsite were chosen as experiment sites. An ant sample, consisting of one ant, was taken from each anthill. The ants were identified by David Wietlisbach as Dorymyrmex bureni. Of the four sites in each area, two sites were shaded from direct sunlight by overhead canopy, and two sites were exposed to direct sunlight. Each investigator collected two sets of data from each site.

Forest Area / Overhead Canopy
Present (P), or absent (A) / Dune Area / Overhead Canopy
Present (P) or absent (A)
Site 1 / P / Site 5 / A
Site 2 / A / Site 6 / A
Site 3 / A / Site 7 / P
Site 4 / P / Site 8 / P

Data were collected on the height and diameter of each anthill. Thirteen additional anthills were measured to characterize the range of anthill sizes typical for the study area (Table 1). In each observation period, we spent 5 min collecting data. During the first min, the number of ants on the anthill were counted and recorded. For the following three min, the ant activity was observed and the number of active ants was recorded. Active ants were defined as ants coming out of the ant-hole carrying sand/debris, depositing it on the hill, and immediately returning to the hole. The total number of ants on the anthill was counted and recorded during the final minute of observation. We collected data concurrently at the two locations (that is, one investigator was at one location while the other investigator made observations at the other location).

DATA

Table 1. Measurements of diameter and height of anthills adjacent to the OssabawIsland campsite.

Diameter (mm) / Height (mm)
Sample / 11.30 / 1.70
Sample / 6.70 / 0.60
Sample / 17.70 / 3.90
Sample / 15.70 / 4.50
Sample / 6.80 / 1.70
Sample / 15.10 / 2.30
Sample / 16.40 / 5.10
Sample / 12.70 / 3.80
Sample / 8.10 / 2.30
Sample / 11.20 / 2.10
Sample / 10.80 / 0.70
Sample / 7.90 / 2.20
Sample / 7.20 / 7.30
Site 1 / 13.40 / 2.40
Site 2 / 11.60 / 2.40
Site 3 / 15.50 / 5.10
Site 4 / 12.40 / 3.60
Site 5 / 16.30 / 5.90
Site 6 / 13.40 / 1.90
Site 7 / 16.40 / 7.10
Site 8 / 14.30 / 4.60
Mean / 12.42 / 3.39
SD (+) / 3.5 / 1.93
Max / 17.70 / 7.10
Min / 6.70 / 0.60

Table 2. Raw data from observations made by each researcher.

Data collected by Brooke.

* See Pictures 1-3 for examples.

Site / Time of day (PM) / Number of ants present / 3 minutes / Number of ants present / Location of anthill
(shade or sun)*
1 / 1:18 / 5 / 147 / 5 / sun/shade
1 / 2:45 / 8 / 142 / 6 / shade
2 / 1:27 / 0 / 0 / 0 / sun
2 / 2:51 / 4 / 96 / 7 / shade
3 / 1:31 / 0 / 0 / 0 / sun
3 / 3:01 / 10 / 75 / 6 / shade
4 / 1:38 / 4 / 99 / 5 / sun/shade
4 / 3:10 / 9 / 83 / 4 / shade
5 / 2:05 / 2 / 51 / 2 / sun/shade
5 / 3:45 / 4 / 53 / 3 / sun/shade
6 / 2:11 / 0 / 0 / 0 / sun
6 / 3:52 / 0 / 0 / 0 / sun
7 / 2:14 / 1 / 26 / 3 / sun/shade
7 / 4:03 / 0 / 4 / 2 / sun/shade
8 / 2:19 / 2 / 9 / 0 / sun/shade
8 / 4:16 / 1 / 37 / 0 / sun/shade

Data collected by Rebecca.

* See Pictures 1-3 for examples.

Figure1. Comparison of experiment sites’ anthill diameter versus the mean diameter of measured anthills.

Figure 2. Comparison of experiment sites’ anthill height versus the mean height of measured anthills.

Figure 3. Total number of active ants, at each site, observed in the sun, shade/sun, and shade.

DISCUSSION AND CONCLUSIONS

We found that most ant activity occurred in shade (751 active ants) and sun/shade (624 active ants). The least amount of activity occurred in sites exposed to full sunlight (49 active ants). Thus, the amount of direct sunlight appeared to influence ant activity. Sites with direct sunlight had little or no ant activity; and sites in partial or full shade had significantly more activity (Figure 3). These findings are in agreement with the results reported by other investigators (Taz 2004). Because ants live primarily underground, they are more active in darkness. Another hypothesis is that the direct sunlight heats the sand soil so ants avoid activity on the hot sand for thermal regulation reasons.

We selected sites with and without canopy to investigate whether this factor had an effect on ant activity. However, as we made our observations, we noted that the presence or absence of canopy did not correlate directly with the anthills exposure to sunlight: the sun moved throughout the observation period, affecting the effectiveness of the overhead canopy in establishing shade.

Our third question focused on the possible relationship between anthill size and the number of active ants. Of the sites we chose for our observations, 6of the 8 anthills were within one standard deviation (SD) of the mean, both for diameter and height. And all 8 were within 2 SD’s. The 8 experiment sites were a representative of other anthills in the area (Figures 1 and 2).

RECOMMENDATIONS

Future research could investigate the relation between anthill size and ant activity. It is likely that anthill size corresponds to the age of the anthill: a larger anthill is probably more established (older), and should therefore contain more ants in the colony. For this reason, it is reasonable to expect a positive correlation between anthill size and the number of active ants.

Further investigation could include collecting data at various times of day and during different season of the year. From our research on ant behavior, we found that various species react differently to sunlight. The ant activity of different species, in response to sunlight, could be compared.

Lastly, additional research could include changing the sun exposure over an anthill. For example, after obtaining data on ant activity of an anthill in direct sunlight, place a small canopy over an anthill to observe if there is a change in activity. From the results in this study, it is reasonable to expect an increase in activity once the small canopy is placed over the anthill. The canopy would shade the anthill; therefore decrease the temperature of the sand soil creating a more desirable work environment for the ants.

ADDITIONAL CONSIDERATIONS

The anthill sites may have been disturbed by people walking and the truck driving near the sites.

There may have been a discrepancy in the interpretation of “ant activity.”

It was difficult to be accurate in counting the ants due to their quick movements.

Other miscellaneous distractions could have affected accuracy in counting ants (swatting at insects and people that were pestering us, wiping sweat from the brow, and other wildlife that caught our attention).

ACKNOWLEDGEMENTS

Dave Wietlisbach provided assistance in identifying the ants taxonomically; Dr. Arthur Stewart assisted in the development of the experiment.

REFERENCES

California Department of Food and Agriculture. (2004). Red imported fire ants. Retrieved on June 13, 2004, from,

Taz’z Antworld. (2004). How to keep your ants happy. Retrieved on June 13, 2004, from,

Cohen, D. L. (2004). Wildlife, nature, and landscape photography. Retrieved on June 13, 2004, from, Macro/Image07.htm.