What is media ant

Messor barbarus - Metacemyia

Messor Barbarus is a species of harvest ant in the subfamily Myrmicinae. It occurs in southern Europe and northern Africa.

Interaction with people

Messor barbarus causes 50– 100% of the seed losses and is the most common ant in arable fields in northeastern Spain (Westerman et al. 2012).


Trail foraging behavior

Messor barbarus acts according to the optimal forage theory, which predicts that the selectivity in ants increases with increasing resource wealth in an area and with increasing distance from the starting point. The trails were also favored differently due to the relative abundance of resources made available to ant populations. Highly trafficked trails had a higher average rate per worker, meaning the harvesters on those trails returned higher resource rates more efficiently. These paths attracted more forage ants to collect overall semen, and the forage ants returned semen at a higher rate per capita. This foraging pattern indicates that the relative abundance of food along different pathways influences the pattern of foraging behavior in Messor barbarus. On long-distance paths, ants exhibit behavior with strong chemical marking on preferred seeds to allow route creation and maintenance.

Recruiting Methods

While the individual harvest is important for times of homogeneously distributed resources at a low level, mechanisms that enable rapid recruitment and mobilization of colonial power in harvesting resource-rich regions enable increased energy gain at the colony level. There are three different methods of mass recruitment in the harvesting of ants.

  • Tandem run: An ant uses chemical or tactile signals to guide a trailer ant to a destination along the path.
  • Group Recruiting: Groups of five to thirty workers each are recruited by senior executives who use an engine gauge to track a short-lived trail of recruiting pheromones. This tactic is often used to retrieve larger items.
  • Mass recruitment: Recruitment Pheromones are separated by choppers and workers leave the nest to follow established paths in relation to the amount of pheromones recruited on a particular track.

M. barbarus uses trunk paths, permanent paths with a length of up to 30 meters, which are preserved even when not in use.

Division of labor in behavior in foraging for food

Small seeds such as oat fragments or Canary Islands seeds are preferred to trigger the onset of recruitment and harvest mobilization in Messor barbarian populations. This is because they allow a faster return on investment between the first discovery of the food source and the subsequent return of the scouts to the nest to relay information to the larger population. The trail is being adjusted by a fleet of early boy scouts who improve the harvesting patterns to select the preferred seed size. Worker ants are divided into three different size classes, which in turn correspond to the size of the seeds harvested. All ants take part in putting away, but there are different roles within the size classes. The majority of ants in the harvest arena are media ants, primarily responsible for putting them away. Smaller ants are most efficient at carrying smaller seeds, such as oat fragments. Main ants are mainly involved in harvesting larger or more preferred types of seeds. The collective action of M. barbarus favors minimizing foraging rather than maximizing the efficiency of energy gain per item harvested. Overall, group collaboration enables a successful balance between the benefits of maximized food utilization and colony-wide energy gain and the costs associated with increased risk to predators.

These different classes of workers cooperate in the transport of many seeds, which often form a transport chain. The first workers are usually small to medium-sized, which corresponds to a high load ratio. Lower loading ratios correspond to the larger workers who tend to orient themselves towards the end of the haulage chain and move the larger goods for the colony. Overall, this strategy reduces the time required to move to the nest and results in a net benefit for the colony.

Selection of the aggregation points

Studies show that the only reliable predictor of ants behavior was the mass of seeds harvested; Seeds weighing less than 0.4 mg were rarely selected. Boy scout ants bring back small seeds during their first harvest as it takes a shorter period of time to get those seeds back into the population. The subsequent selection of aggregation sites does not depend on a direct comparison between potential sites by a single scout, but on mechanisms of chemical traces that enhance recruitment for traces with higher yields. The net result of this is that, given a variety of options for aggregation sites, colonies search for food differently in resource-rich regions. This behavior results from a collective decision on behalf of the group made by independently acting people in the population. M. barbarus also stops searching for food at an aggregation point when the food supply is exhausted.

Interactions with neighboring ant populations and seed theft

Occasionally, when a colony crosses en route or seeds enter the regions of other colonies, violent fighting often ensues. Ants harvesting seeds usually direct the pathways specifically to avoid disrupting other colonies' pathways to harvesting seeds, as conflicts are likely to affect the colony's ability to maximize harvesting efficiency. In some cases, the interference competition takes place through robbery within the population. One study found that Messor Barbarus populations harvested Euphorbia characias seeds from other ant populations, particularly populations of Tapinoma nigerrimum. This behavior is relatively common and is achieved by removing the harvested seeds directly from the migratory ant populations, or through more indirect territorial defense mechanisms, reporting and dealing with physical threats, chemically induced deterrents, and nests plugging. The behavior has implications for the processes of recruiting seedlings for E. characias, which depend on myrmecochory and seed distribution by ants to transport their seeds to suitable locations for survival and reproduction.

Harvest as weed control in cereal crops

M. barbarus is a seed predator on grain fields. This is beneficial to plants as it serves as a form of weed control. There is some evidence that this harvest may result in a decrease in the overall yield from the harvest. However, studies show that the actual impact of this hypothesis is minimal, with only an average of 0.2% decrease in potential yield due to seed predation in newly sown seed populations and an average of 0.6% decrease in yield losses at harvest. Therefore, the negative impact on yield is outweighed by the benefits to the crops from the weed control function of the harvesters.


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