Sanika Gupte and Vaishali Somani*
Zoology Department, R. Jhunjhunwala College, Ghatkopar, Mumbai- 400 086
*Zoology Department, Maharshi Dayanand College of Arts, Science and Commerce, Mumbai-400012
Ant nests are a form of shelter that protects the ants from their enemies and the environment around them, including the weather. They also provide a suitable place for the ants to safely rear their brood and to keep their queens protected. Without their nests most ant colonies would die out very quickly. The present study attempts to understand establishment of Harvester ants colony in post monsoon period in year 2014-2016 near agricultural fields of Mulshi, Maharashtra. Harvesters are preliminarily seed collecting ants. About thirty nests were recorded. Most ant nests are made in damp soil and can be several feet in depth and circumference. Though shifting of nest location is very common in some ants, present study shows activity in most of the nests. Less anthropogenic activity and availability of food from surrounding agricultural fields appear to be favorable factors for the establishment of this colony.
Keywords: Harvester ants, nests, soil, seeds.
Ants ( Hymenoptera, Family- Formicidae) are social insects forming large societies. They construct nests in various suitable habitats including trees, dead wood logs, under large stones, crevices or construct underground interconnected chambers. The underground nests show the entrance on the soil surface, sometimes protected by leaf litter or aggregation of soil particles around it. Amarsinghe (2010) has described subterranean nests with above ground mound or cone surrounding the nest entrance. Various ant nests are reported from urban garden in Mumbai.(Khotet al, 2013) Harvester ants (Fig 1) are known to have elaborate underground nests facilitating seed storage. The observation of such nests gives an idea about the peculiar feeding habits and territoriality. It may also be helpful to understand how the ants respond or adapt to the environmental conditions in the habitat.
Materials and method
The present study was carried out in an agricultural area in Mulshi Tehsil of Pune District, Maharashtra. This area is near village Male (18.500 N, 73.510 E)and is characterized with paddy cultivation. Observations with respect to Harvester ant nests were recorded from 2014 to 2016. This included measurement of area occupied by each nest, measurement of distance between neighbouring nests and recording the raised walls around the nest entrances.
In the initial period of study, premonsoon season of 2014, the number of nests was five. The nests were located not far from each other and were not recorded on the other side of the paddy field. Though few other varieties of ants were recorded in the area, none of them exhibited such conspicuous and elaborate nests. The number slowly increased and reached 30 at the end of monsoon in 2016. (Table-1).
Result and Discussion
Increase in the number of nests indicated that these Harvester ants are efficiently using the available food resources, resulting in the rapid increase in the members of the colony.
The raised walls of the nests are acting as protection against the heavy rainfall of the region with average 2841 mm.The Western Ghats are known for such rainfalls and this is an excellent adaptation displayed through nest architecture. In some of the nests, the concentric walls were found broken or flattened after certain period. However there were no confirmed records of the repairing done. The number of raised soil walls or circles varied between 3 to 8. Though most of the nests did not show vegetation growth within their areas, some of the nests were completely covered with grasses. The distance between the neighbouring nests varied from 2.2 meters to 11.6 meters.
Such type of nests are recorded in other regions of Maharashtra including Mumbai, Tansa Wild life Sanctuary (personal observations by the authors), Radhanagari (http://www.myrmecos.net/2015)
Some ants are considered as generalist feeders (Narendra Ajay and Kumar Sunil, 2006) whereas harvester are known to store the seeds. (Narendra Ajay and Kumar Sunil, 2006)About 27% of the nests showed heaps of husks indicating active seed collection. 23% nests showed display of insect body parts including ants and termites. These included bodies of Camponotus sp., also recorded in the study area. There is a presence of termite mound near the harvester ant nestings. The body parts of termites near the ant nests indicated probable use of termites as food resource by these ants.
The activity of the workers was recorded in all the nests. The number of workers entering the nest or leaving the nests were recorded for fixed intervals with several repeated observations spread over the entire day during premonsoon and postmonsoon period. The intensity was lower during the period of direct sunlight. However during cooler time of the day, the activity of foragers showed marked increase. The average number of workers in four representative nests are shown in Graph 1.
Easy access to the paddy field and other grasses in the area must be a favorable condition for this harvester ant colony. This colony appeared to be Multiple Nest Colony as suggested by Robinson (2014). This polydomy could increase the size of the colony efficiently as more and more nests were added. This probably helped distribution of foragers across the available area to achieve more food and reduce competition with other insect competitors including nonrelated ant species of the area. No territorial conflicts were recorded among the workers of different nests. However these observations about territoriality were opportunistic and not of regular nature.
The presence of these nests thus act as an example how the ants establish themselves as rapidly growing social colony adapted to the given set of environmental condition. Such colonies may in turn influence the soil characteristics and other biota of the area, linked to these ants through the food web.
The authors are thankful to The Principal and Staff members of Zoology Department, R. Jhunjhunwala College and MaharshiDayanand College of Arts, Science and Commerce, Mumbai for their continuous support.
Table 1- Harvester Ant Nests near Pune
|Nest Numbers||Approximate Area (in cm2)||Distance from the neighbouring nest (in m)||No. of concentric whorls or raised walls|
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