Messor barbarus

Appearance

The Queen has a black thorax and reddish brown to black head. She is 15 - 18mm in size.
This species has quite a diverse range in size for the workers. They are shiny black in colour but major workers can have a reddish brown head. They range in size from 3-14mm.
Males are black in colour and are 7-8mm in size.
This species does not have a soldier caste, despite the size of the major workers.

Distribution

On occasions when a colony intersects in path or places seeds in the regions of other colonies, violent fighting often breaks out. Seed-harvesting ants ordinarily will thus direct paths to specifically avoid disrupting the paths of other seed-harvesting colonies, as engaging in conflict is likely to detract from the colony’s own ability to maximize harvesting efficiency. In some instances, interference competition plays out through intra-population seed robbery. One study indicated that ''Messor barbarus'' populations rob harvested ''Euphorbia characias'' seeds from other ant populations, specifically populations of ''Tapinoma nigerrimum''. This behavior is relatively common, and is accomplished by directly removing the harvested seeds from the traveling ant populations, or through more indirect mechanisms of territory-defense, physical threat displays and altercations, chemically induced deterrents, and nest-plugging. The behavior has impacts on the processes of seedling recruitment for ''E. characias'', which depends on myrmecochory, seed dispersal by ants, to transport its seeds to appropriate sites for survival and reproduction.

Behavior

''Messor barbarus'' is found to act in accordance with the optimal foraging theory, which predicts that selectivity in ants increases with increasing richness of resources in an area, as well as with increasing distance from starting location. Trails were likewise differentially favored according to the relative abundance of resources provided to the ant populations. Highly frequented trails had a higher mean rate per worker, meaning the harvesters returned higher rates of resources more efficiently along these trails. These trails drew more foraging ants to retrieve seeds on the whole, and the foraging ants returned seeds at a higher rate per capita. This foraging pattern indicates that relative food abundance along varying trails impacted the patterns of trail foraging behavior in ''Messor barbarus''. For trails spanning long distances, ants exhibit behavior of strong chemical marking on preferred seeds to allow for the creation and maintenance of the route.Small seeds, such as oat fragments or canary seeds, are favored for triggering the onset of recruitment and mobilization of harvesting in ''Messor barbarus'' populations. This is because they allow for a faster rate of return between the initial discovery of the food source and the subsequent return of scouts to the nest to relay information to the greater population. The trail is adjusted by a fleet of initial scouts which enhance the harvesting patterns to select for the preferred seed size. Worker ants are divided into three distinct size classes which in turn correspond to the size of the seeds harvested. All of the ants participate in the process of trail-laying, but within the size classes there are distinct roles. The majority of ants in the harvesting arena are Media ants, which are responsible primarily for trail-laying. Minor ants are most efficient in carrying smaller seeds such as oat fragments. Major ants are primarily involved in the harvesting of larger or more preferred seed species. The collective action of ''M. barbarus'' favors the minimization of foraging time rather than maximized efficiency of the energetic gain per item harvested. On the whole, group cooperation allows for a successful balance to be struck between the benefits of maximized food exploitation and colony-wide energy gain and the costs associated with increased predation risk.

These different classes of workers cooperate to transport loads of seeds, often forming a transport chain. The first workers tend to be smaller to medium-sized, which corresponds to a high loading ratio. Lower loading ratios correspond to those larger workers which tend to align towards the end of the transport chain, transporting the larger goods for the colony. Overall, this strategy reduces time spent in transport to the nest and results in a net benefit to the colony.

Habitat

This species lives in sandy and shrubbed areas - often in close proximity to seed bearing plants.

Food

This species is a highly granivorous ant which collects all kinds of small seeds and chew them into so called 'ant bread'. Most of their water requirements are covered by seeds and insects.

Defense

''M. barbarus'' is a seed predator in cereal fields. This is beneficial to crops, as it serves as a form of weed control. There is some evidence which indicates this harvesting can lead to a decline in total yield at harvest. Studies show however that the real effects of this hypothesis are minimal, with only an average of a 0.2% decline in potential yield from seed predation in newly sown seed populations and an average of a 0.6% decline in yield losses at harvest. Thus, the negative impacts on yield are outweighed by the benefits to crops through the weed control function of the harvesters.