Cleaning ants are successful

Metarhizium fungus makes fewer victims

Argentine ant removes sporen of Metarhizium fungus

Ants defend themselves against disease-causing Metarhizium fungus by grooming off fungal spores from each other. Prolonged exposure to that cleaning behaviour makes the fungus less deadly, Miriam Stock and colleagues show.

Metarhizium fungus can quickly spread throughout an ant nest because the ants easily infect each other with fungal spores. But the animals take action to inhibit the pathogen. That does not leave the fungus unaffected, Miriam Stock and colleagues show with experiments.

To counteract the fungus, ants can disinfect nest and brood (eggs, larvae and pupae) with a mixture of formic acid, which they produce in a poison gland, and tree resin. In addition, a sick ant stays away from the brood and spends more and more time outside the nest so as not to endanger its nest-mates. And the animals keep each other clean. If spores of the fungus land on an ant, her nest-mates either groom off the spores, risking infection themselves, or spray them with formic acid.

New spores

These caring nest-mates should act quickly. The spores attach on the affected ant and germinate, after which nothing can be done anymore. The fungus penetrates the body to develop, eventually killing the ant. Then the fungus appears on the cadaver forming spores that make new victims in the next infection cycle.

Conducting experiments with the Argentine ant, Linepithema humile, Stock shows that timely care does indeed help; the presence of other ants reduces the chance that an ant dies after contact with fungal spores.

But, as it turns out, cleaning also causes changes in the fungus.

Metarhizium-fungus adapts

The trials consisted of series in which the Metarhizium fungus passed repeatedly via spores from a dead ant to a new victim. In half of these series, the infected ant was held isolated, in the other half she was accompanied by two nest-mates that could remove the fungal spores. Conducting a final test after ten infection cycles, the researchers allowed the fungus to infect either an isolated ant or an ant with company.

In the final test, fungal lines that had grown on isolated ants caused a lot of mortality among newly infected ants when they did not receive care from others. But fungal lines that had infected ants that were in company of other ants – that could groom them -, had changed. They formed twice as many spores, but nevertheless made fewer victims among ants they came into contact with, even if there were no nest-mates around to help. These fungal lines had become less deadly.

Essential component

And there was something else: the spores of those ‘social fungal lines’ were less well detected and removed by the ants. The researchers discovered that these spores produced less ergosterol; this is a compound that occurs in all fungi and that, apparently, arouses the ants. So, the ‘social fungus lines’ evade defence by the ants.

But this comes at a cost. Ergosterol is an essential component of the spore membrane. The fact that the ‘social lines’ have lower levels of this important component probably explains why they are less deadly.

So, grooming each other to remove Metarhizium fungus spores as ants do is useful in two ways. It works immediately if ants quickly remove spores from a nest-mate, saving her from death. And in the longer term, it makes the fungus less dangerous.

Willy van Strien

Photo: Argentine ants exchanging food. Davefoc (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

See also: ants disinfect their nest with a mixture of resin and formic acid

Stock, M., B. Milutinović, M. Hoenigsberger, A.V. Grasse, F. Wiesenhofer, N. Kampleitner, M. Narasimhan, T. Schmitt & S. Cremer, 2023. Pathogen evasion of social immunity. Nature Ecology & Evolution, online February 2. Doi: 10.1038/s41559-023-01981-6
Brütsch, T., G. Jaffuel, A. Vallat, T.C.J. Turlings & M. Chapuisat, 2017. Wood ants produce a potent antimicrobial agent by applying formic acid on tree-collected resin. Ecology and Evolution 7: 2249-2254. Doi: 10.1002/ece3.2834
Bos, N., T. Lefèvre, A.B. Jensen & P. D’Ettore, 2012. Sick ants become unsociable. Journal of Evolutionary Biology 25: 342-351. Doi: 10.1111/j.1420-9101.2011.02425.x
Chapuisat, M., A. Oppliger, P. Magliano & P. Christe, 2007. Wood ants use resin to protect themselves against pathogens. Proceedings of the Royal Society B 274: 2013-2017. Doi: 10.1098/rspb.2007.0531

Sponge sneezes to stay clean

Stove-pipe sponge prevents clogging of filtration system

Stove-pipe sponges sneezes to keep the filtration system clean

The water from which sponges filter their food also contains oversized and inedible particles. Niklas Kornder and colleagues show how the stove-pipe sponge gets rid of this rubbish.

Sponges are one of the oldest animal groups, and perhaps the oldest. They are simple animals, without organs. Niklas Kornder and colleagues discovered that such simple organisms can keep their body clean.

To obtain food, sponges filter the water in which they live. Water is drawn in through small inlet pores – the ostia – and passes through an internal canal system, where food particles are extracted. It leaves the sponge through larger outflow openings – the oscula.

But water not only contains suitable food particles, but also large chunks and inedible stuff. It was assumed that this waste would be shed with the outflowing water. Kornder now shows that this is not true. It would be risky, as the rubbish may clog the filtration system.

Mucus highways

The researchers investigated the cylindrical stove-pipe sponge, Alpysina archeri, which lives in the Caribbean Sea, and video-recorded how it expels waste. It is a large sponge that can grow to a length of one and a half meters.

In the internal canals, waste is embedded in mucus, as it turns out. That mucus is transported to the inlet pores and exits, accumulating at the sponge surface. So, it moves against the direction of the water flow through the canals. On the sponge surface, a weblike pattern of ‘mucus highways’ can be seen, over which mucus streams travel. The streams aggregate into clumps on slightly elevated junctions.


From time to time, a wave of contractions and relaxations propagates across the sponge surface, while the inlet pores are closed: the stove-pipe sponge is sneezing. During the sneeze, the mucus clump is shed off, the sponge getting rid of the waste. And small fish and other animals that live in the vicinity of the sponge enjoy a meal.

The researchers think that other sponges also sneeze to keep themselves clean. However, it is still unknown by what mechanism waste laden mucus is transported.

Willy van Strien

Photo: Aplysina archeri, stove-pipe sponge. Nick Hobgood. (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Watch the sneezing sponge on video

Kornder, N.A., Y. Esser, D. Stoupin, S.P. Leys, B. Mueller, M.J.A. Vermeij, J. Huisman & J.M. de Goeij, 2022. Sponges sneeze mucus to shed particulate waste from their seawater inlet pores. Current Biology, online August 10. Doi: 10.1016/j.cub.2022.07.017

Acid gulp

Ant swallows its own formic acid to stay healthy

Tnaks to formic acid, Formicinae ants are healthy

Formic acid appears to be a great help for ants to prevent infection from contaminated food, Simon Tragust and colleagues discovered. A gulp after each consumption increases their survival chance.

People like sweet desserts, but for ants of the subfamily Formicinae it is different. They take a gulp of formic acid after eating or drinking, Simon Tragust and colleagues witnessed.

This is remarkable, because formic acid is an aggressive substance. Formicinae ants produce it in a venom gland that has an opening at the tip of the abdomen. They were known to spray it at predators, such as birds, spiders, and insects, to defend themselves, and this is understandable. But swallowing?


Tragust and colleagues had shown previously that Formicinae ants use their acid not only against predators, but also against pathogens. Workers apply it in combination with resin to keep an entomopathogenic fungus (Metarhizium brunneum) out of their nest.

Also, they use formic acid to keep the brood clean. If they detect pupae covered with spores of the pathogenic fungus, they clean them and cover them with formic acid, which they had taken up from the abdominal gland opening into the mouth.

If fungal spores have already germinated on a pupa and the fungus has penetrated the cuticle, workers unpack the infected pupa from its cocoon, bite holes in the skin and inject formic acid. In this way, they prevent the fungus from growing and forming spores that will contaminate the rest of the colony. The pupa does not survive the treatment, but it would have been killed by the fungus anyway.

Crop acidity

Now, a new application of formic acid comes to light: Formicinae ants swallow their own formic acid after eating or drinking something. Tragust deduces this from tests in the lab with Florida carpenter ant, Camponotus floridanus. He offered ants honey water or plain water and saw them lick their abdominal tip afterwards. Apparently, they then took up acid into the mouth and swallowed it, as Tragust showed that the contents of their crop, just before the stomach, became very acidic.

Perhaps, the idea was, workers take formic acid to kill bacteria that may be present on food. And that was the case, as became clear from tests in which workers were given food that was contaminated with a pathogenic bacterium species (Serratia marcescens). In ants that then took a gulp of formic acid, bacteria did not survive the crop environment and the rest of the intestinal system remained clean. Ants that were prevented from taking in acid, were at greater risk of a deadly infection.

Only bacteria that thrive in acidic environments survive the acidic crop, and such bacteria populate the ants’ intestines. But these are beneficial bacteria that help digest food. The acid appears to be an excellent remedy against pathogenic microbes.

Fortunately, we don’t have to take an extremely sour dessert like Formicinae ants, because our stomach keeps itself acidic.

Willy van Strien

Photo: Carpenter ant, Camponotus cf. nicobarensis. ©Simon Tragust

Ants also use formic acid to keep fungus out of nest

Tragust, S., C. Herrmann, J. Häfner, R. Braasch, C. Tilgen, M. Hoock, M.A. Milidakis, R. Gross & H. Feldhaar, 2020. Formicine ants swallow their highly acidic poison for gut microbial selection and control. eLife 9: e60287. Doi: 10.7554/eLife.60287
Pull, C.D., L.V. Ugelvig, F. Wiesenhofer, A.V. Grasse, S. Tragust, T. Schmitt, M.J.F. Brown & S. Cremer, 2018. Destructive disinfection of infected brood prevents systemic disease spread in ant colonies. eLife 7: e32073. Doi: 10.7554/eLife.32073
Tragust, S., B. Mitteregger, V. Barone, M. Konrad, L.V. Ugelvig & S. Cremer, 2013. Ants disinfect fungus-exposed brood by oral uptake and spread of their poison. Current Biology 23: 76-82. Doi: 10.1016/j.cub.2012.11.034

Defensive cocktail

Ants produce powerful antibiotic by mixing resin with acid

Formica paralugubris produces powerful antifungal agent

Workers of the wood ant Formica paralugubris are skilled poisoners. By treating tree resin with formic acid, they produce a powerful disinfectant to control a pathogenic fungus, Thimothée Brütsch and colleagues show.

Pathogenic micro-organisms, such as the common entomopathogenic fungus Metarhizium brunneum, pose a continuous threat to ant nests; because the ants live close together, the risk of epidemics is high. Therefore, ants should keep their nests hygienic.


And so they do. Workers of the alpine wood ant Formica paralugubris, for instance, incorporate large amounts of solidified resin from coniferous trees, especially spruce, into their nest to fight pathogens, as Michel Chapuisat showed. The distinctive smell of tree resin comes from terpenes and other volatile substances; these are compounds that decrease bacterial and fungal load in wounded trees. And within ant nests, they do as well. In the presence of resin, bacteria and fungi are inhibited, with the result that more larvae survive when exposed to Metarhizium, and adult ants and larvae have a higher chance to survive when a detrimental bacterium invades the nest.


Now, Thimothée Brütsch and colleagues report that the ants enhance the antifungal activity of the resin considerably by applying formic acid. This acid, which the ants produce into their venom gland, has an antiseptic effect in itself, just like the volatile substances from resin. But the mixture of the resin with formic acid seems to work particularly well; it has greater antifungal activity than you would expect from the separate effects of resin and acid. This means that the acid increases the disinfectant effect of the tree resin.

So, the ants not only collect pieces of resin to disinfect their nest and protect themselves against pathogens, but they also treat it with formic acid to obtain a more powerful antimicrobial agent.

Willy van Strien

Photo: © Timothée Brütsch

Brütsch, T., G. Jaffuel, A. Vallat, T.C.J. Turlings & M. Chapuisat, 2017. Wood ants produce a potent antimicrobial agent by applying formic acid on tree-collected resin. Ecology and Evolution, online March 6. Doi: 10.1002/ece3.2834
Chapuisat, M., A. Oppliger, P. Magliano & P. Christe, 2007. Wood ants use resin to protect themselves against pathogens. Proceedings of the Royal Society B 274: 2013-2017. Doi: 10.1098/rspb.2007.0531