Metapleural glands (also called metasternal or metathoracic glands) are secretory glands that are unique to ants and basal in the evolutionary history of ants. They are responsible for the production of an

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...

fluid that then collects in a reservoir on the posterior of the ant's alitrunk. These reservoirs are also referred to as the bulla and vary in size between ant species and also between castes of the same species. From the bulla, ants can groom the secretion onto the surface of their

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...

. This helps to prevent the growth of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

and fungal spores on the ants and inside their nest. Though considered an important component in an ant's

immunity Immunity may refer to: Medicine * Immunity (medical), resistance of an organism to infection or disease * ''Immunity'' (journal), a scientific journal published by Cell Press Biology * Immune system Engineering * Radiofrequence immunity de ...

against parasites, some ant species have lost the gland during their evolution. These losses correlate with ants that have a 'weaving' lifestyle, such as ants in the genus '' Oecophylla'', '' Camponotus'' and '' Polyrhachis''. It was originally suggested that because this weaving lifestyle also tended to involve an arboreal lifestyle, the parasite pressure above ground was not as great as for terrestrial ants, resulting in a reduced

selective pressure Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...

to keep this antibiotic gland. Recent work suggests instead that these ants may just use other antiparasite defences such as increased grooming and venom. Most male ants are not known to have metapleural glands. It is believed that they benefit from the shared secretions of ant workers and do not need any themselves. Additionally, slave-making ants do not have metapleural glands, though the slave species they use do and it is these ants that groom the slavemakers and their brood.

References

{{Reflist, 32em Insect anatomy Arthropod glands Myrmecology