Night owls or morning larks? Study of food retrieval by Solenopsis geminata ants

Gayathri R

University of Hyderabad, Gachibowli, Hyderabad, Telangana 500046

Dr. Priyadarsanan Dharma Rajan

Ashoka Trust for Research in Ecology & Environment, Bengaluru 560064

Abstract

Ants are eusocial insects that exhibit a diverse behavioural repertoire, often owing to their direct interaction with the environment that they live in. While the coordinated behaviour of foraging individuals from a colony is highly fascinating, the presence of numerous members makes it a highly complex collective process. Foraging in ants includes both activities of individual ants as well as that of the behaviourally combined groups. This ground activity is affected by a variety of factors; both intrinsic and extrinsic which have short term and long term effects on their behaviour. Changes in the foraging activity across day and night shall be highlighted in this project. The main objective is to study and compare the foraging frequency and transport velocity of Solenopsis geminata across different times during day and night. It is expected that the variation in parameters like humidity, temperature and light intensity levels in a rhythmic manner shall have a direct effect on the ground activity of these subterranean insects. While light intensities may aid in visual navigation, ambient temperature may regulate metabolic activity and yet other circadian factors like changes in humidity and other elements of nature may affect the foraging efficiency of ant colonies. Through detailed observation of aspects like exploratory distance, foraging frequency, visit duration and transport velocity across different times of the day, I shall study the foraging behaviour of this ant across day and night.

 Keywords: ant behaviour, circadian rhythm, foraging, light, temperature

INTRODUCTION

Background/Rationale

Gayathri R

Ants belong to the family Formicidae and approximately 22,000 ant species are estimated to be present in the world. They are the most common and extremely interesting insects that display many unique abilities. Colonisation of ants in almost every landmass on earth and their success of thriving in varying environmental conditions has been attributed to their eusocial nature, ability to adapt to modified habitats, exploit resources and defend themselves. Their social behaviour- division of labour, communication between individuals and many other organised behaviour has been an extensive subject of study. Their integrated behaviour during food searching is very fascinating. Foraging in ants is a complex and collective process which includes both activities of individual ants as well as that of the behaviourally combined groups. This ground activity is affected by a variety of factors; both intrinsic and extrinsic which has short-term as well as long-term effect in the behaviour. This can be explained as a function of numerous individual components and properties (​​Traniello, et al, 1989​​). So, this broad behaviour can be broken down into individual components like foraging distance, walking velocity, frequency and duration of foraging ( ​​G. C. Dibley, 1974​​). Changes in the foraging activity in the presence and absence of light is being highlighted in this project. It is expected that light’s presence or absence will have a direct effect on the ground activity. This may be because some ants may be oriented visually and availability of light would be advantageous for them to carry out foraging in an easier way. Also, light is directly related to temperature. Increased temperature levels may increase the body temperature of the ants as they are poikilothermic, thereby, resulting in a rise in the metabolic activity which makes them come out of the nest in search of food. Previous studies have looked at how foraging is affected by different weather conditions and seasons (​​Walter R. Tschinkel, 1987​​). The diel rhythm of foraging has also been studied.

Description of Solenopsis geminata: Solenopsis geminata is a ubiquitous ant which is 3-5 mm long. The body is orangish brown and it has a brown head. These ants are highly invasive and are known to have the potential to devastate native ant populations. It presents a great threat to conservation values as it invades native communities. They respond aggressively by stinging to any disturbance caused to them. It usually thrives in hot arid regions. Cold climates are quite unsuitable for them. S. geminata prefers food with high protein content. The diet also includes many human foods rich in carbohydrates. The oldest ants in the colony are the foragers.

Objectives of the Research

Overall objective

1.     To study and compare the foraging behaviour of Solenopsis geminata across different times during day and night.

2.     To examine whether the foraging frequency is higher during the day or night.

3.     To compare the individual components like transport velocity, frequency and duration of visit across day and night using statistical methods.

METHODOLOGY

Methods

Nests of Solenopsis geminata were located by providing a food source, observing their trails and tracing their path. Multiple nests were found. 

Experiments were conducted to know the food preference of the ants. 

Trial experiments were done to find out the exploratory distance (the distance range was kept constant). 

0.82 grams of chocolate was provided at a distance of 40 cm - 60 cm. 

Initial conditions like humidity and temperature were noted. 

Times at which the first as well as successive ants arrived were recorded. 

Duration that the ants spent at the food source and the time it reached back to its nest were noted down.

Walking velocity was calculated from the displacement between food and nest and the time it took to reach the nest from the food site. 

Visit duration was computed from the visit time and departure time of each ant. 

Number of ants coming out from the nest in a 15 minute window was noted down.

Above processes were carried out during day and night for different timings. 

Data was analysed by non-parametric analysis using Mann-Whitney U test and have been presented using box plots. 

Graphs were plotted between: 1. Velocity and visit duration

2. Velocity and visit time

3. Visit duration and visit time

4. Start time and velocity

And correlations between these components were studied.

LIMITATIONS: 

1.     During afternoon times, the chocolate often melted. It was difficult to discern whether the returning ants were unladen or carrying the melted chocolate towards the nest. (However, the working definition for our project was that if an ant spent more than 5 s at the food source before returning to the old nest, then it was considered a transporting ant)

2.     Other species of ants were interfering with my ants of interest. This problem was tackled by keeping the food source in such a place where no other ant species’ nests were present.

3.     Night observations were only made from 6:30-7:30 PM as compared to the day observations where the observation period ranged from 11 AM - 4 PM.

Fig 1 Solenopsis geminata ants feeding on chocolate

OBSERVATIONS

Day observations:

Night observations:

Purpose

VISIT DURATION (DAY VS NIGHT)

The visit duration of Solenopsis geminata during day (51.41∓20.93s) is only marginally different from the visit duration during night (42.15∓17.63s; Mann-Whitney U test, N₁ =39, N₂ =13, U =167.5, p =0.07)

Fig 2 Box plot comparing the time spent by the ant at the food source in seconds(s) during day and night

VELOCITY (DAY Vs NIGHT)

The transport velocity of Solenopsis geminata during day was found to be 1.12∓0.62 cm/s and this was significantly lower than the transport velocity during night (0.68∓0.22 cm/s; Mann-Whitney U test, N₁=39, N₂ = 13, U= 144, p=0.02)

Fig 3 Box plot comparing the transport velocity of ants in cm/s during day and night

FREQUENCY (DAY Vs NIGHT)

The number of ants coming out of the nest during day time for a 15 minute observation window (7.8∓2.48) was found to be higher as compared to night (2.6∓2.79; Mann-Whitney U test, N₁=5, N₂ = 5, U= 2, p=0.03)

CORRELATION

1. VELOCITY AND VISIT DURATION

Fig 4 Graph showing relationship between transport velocity of ants in cm/s and duration of visit in s.

No considerable correlation

2. VELOCITY AND VISIT TIME

Fig 5 Graph showing relation between transport velocity of ants in cm/s and visit time in min

There is a negative correlation between velocity and visit time.

3. VISIT DURATION AND VISIT TIME

Fig 6 Graph showing relationship between visit duration in s and visit time in min

No correlation observed

4. START TIME AND VELOCITY

Fig 7 Graph showing relationship between transport velocity in cm/s and the starting time of foraging in min

A slight negative correlation is observed.

REMARKS:

1. On 07-06-2019, when food source was kept at two different distances during night, 52 cm (6:40 PM) and 42 cm (7:00 PM) respectively, no ants turned up. However, when the food source was kept at a distance of 15 cm (7:20 PM) from the nest, few ants came out.

Date: 07-06-2019

Temperature: 25 °C

Distance from the nest to the food source: 15 cm

Place: ATREE

2. On 27-06-2019, the night observation was done an hour after a slight drizzle.

CONCLUSION AND RECOMMENDATIONS

Conclusion

Changes in light intensities did affect the ground activity of Solenopsis geminata ants. Workers did not exhibit tendency to forage at night. Walking velocities of ants were relatively higher in day as compared to night. During night, ants walked much slower. This may be because their metabolic activity may be higher during day time (when the temperature is high). Also, the number of ants coming out of the nests were higher during day than in night. The frequency was very low or zero during night. Low temperature limited the ground activity. However, the visit duration of ants in both day and night was almost similar. They spent around same time on the food source on both times of the day. All these results were obtained in a short term study. Whether these results are consistent for longer periods and across different climatic conditions and long-term micro environmental factors remains to be investigated through future studies.

REFERENCES

1. ​G. C. Dibley, 1974​

2.​Walter R. Tschinkel, 1987​

3. ​Traniello, et al, 1989​

ACKNOWLEDGEMENTS

Foremost, I would like to express my sincere gratitude to my guide Dr. Priyadarsanan Dharma Rajan for his motivation and immense knowledge during my project.

Besides, I would like to thank Dr. Anoop Karunakaran. I could not have imagined having a better mentor for my study. I am grateful to him for enlightening me the first glance of research with his constant support, guidance, encouragement, insightful comments and enthusiasm.

I owe a lot to Dr. Seena Narayanan, Aswaj, Sneha and all lab members for being so cooperative and helpful.

I would also like to acknowledge the crucial role of IAS for selecting and enabling me to do the fellowship.

At last but not the least, huge thanks to my parents and sibling who were and are always there for me.