Sizes of anthills

On the former pasture Stabelchod in the Swiss National Park exists a large density of anthills. At that place, around 1'600 ant nests have been discovered and documented so far and therefore is this pasture a perfect place to study individual influences on the nests in more detail. We have asked ourselves, whether the distance between the forest edge and the ant nest influences the size of the anthill. We are also looking at other aspects in this fieldwork. Whether there is a difference between the wood ant (Formica) and the excised wood ant (Formica exsecta), the sky orientation or the sunlight exposure.

The goal is to find out, if these different aspects have an influence on the size of the anthill. The hypothesis is that the anthills become smaller the further away they are from the edge of the forest. The reason for this is that, according to the Swiss National Park, the ants regulate the internal temperature of the mound with its size. This means that ants build larger mounds in colder places to maintain a temperature between 25°C and 29°C.

The anthills were analyzed in different attributes:

• Location
• Distance to the edge of the forest
• Diameter of the anthill
• Height of the anthill
• Size of the anthill
• Orientation (N, NE, E, SE, S, SW, W, NW)
• Aspect (exposed, half shaded, shadowy)

The location was defined by the app  https://survey123.arcgis.com . Diameter and Height of the anthills were determined by hand with a scale and the size was automatically calculated with the formula for a cone:  1/3 · π · r ²  · h. The sky orientation was figured out with the app  https://play.google.com/store/apps/details?id=com.ktwapps.digitalcompass  and the aspect was determined by our own judgment of how much the anthill was exposed in the sun: Exposed all day long: exposed, exposed to a certain degree: half shaded and almost always in the shadow due to trees, bushes etc.: shadowy.

A total of 44 anthills were analyzed and measured, which were all located on the pasture Stabelchod. In the following, the results are being discussed and analyzed.

This map shows how big the measured anthills were: the bigger the orange circle, the larger the anthill.

This map here illustrates the two different main types of ants which were found and classified. The points are in three colors and red stand for wood ant, blue for excised wood ant and green displays the ants which weren't really sure of or couldn't say what they were.

It seems like the anthills, that are closer to the edge of the woods are larger than the ones on the pasture. But this is not entirely correct: The few fully shadowed anthills aren't much bigger or not bigger at all than the ones which were on a half shaded location.

What was also noticed is, that all the anthills are oriented to the south. We can assume that the reason for this is longer and more intense sunlight. This orientation allows the ants to build a smaller anthill and absorb the same amount of heat energy. This orientation is also suitable due to the geographic location, as the slope faces south. The excised wood ants also seem to build flatter hills compared to the forest ants, since they especially live in open and sunny places like a pasture.

We cannot say with these results of us, if our hypothesis is right or wrong. We just have too unaccurate and too little samples to fully reject or support the hypothesis.

Our results are certainly not totally correct and accurate due to different and sometimes controllable or not so controllable aspects:

• age of the anthills
• types of ants
• the real sunlight exposure
• measurement errors
• form of the anthills

It should be remembered that the results of the fieldwork could be distorted by various factors and these could lead to measurement errors. For example, we did not consider the age of the ant nest and we questioned whether the age of the nest had a direct influence on the size of the mound. Another factor is that we only made a rough estimate of the shade. We distinguished only from exposed, half-shaded and shadowy. It would have been better if we had installed a light sensor and measured the light exposure that way. In addition to this, different species exist in the pasture of Stabelchod. We have only distinguished between the wood ant, excised wood ant and others. It must be kept in mind that we are not trained in this field, and we might have confused the two species sometimes. Another point would be the measurements of the height and diameter of the hill with the help of a scale. It could be possible that the measurements with this method are not always accurate to the centimetre. Also, the anthills did not always have the same cone shape. Some had a more distinct point and others had almost none. This distorted the volume of the mounds because we were only calculating with the normal cone formula. To fix this problem, we should have used different formulas for the different anthills.

Of course was the lack of time we had also the biggest part of our errors due which we had to limit ourselves to simple apps on our phones and estimations. For future researches in this field should the aspects, which had errors in our research, be more specific. Avoiding errors in these aspects is a very important part to get a fully and accurate answer to our hypthesis.