How do ants deliver their poison

How ants protect the offspring from their toxic cleaning agents

Vienna - If you share a house with hundreds of thousands of other people, you would do well to pay attention to cleanliness. So it's no wonder that ants are considered extremely clean animals: When the small insects move into a new nest, they first spend several days cleaning the accommodation thoroughly. They also use a very potent disinfectant: formic acid. Although the substance keeps the nest clean, its use is not without risk, as it can kill unprotected brood. Now researchers led by Sylvia Cremer and Christopher Pull from the Institute of Science and Technology Austria (IST Austria) have found that the silk cocoon protects the sensitive dolls from the negative effects of formic acid.

Many ants produce extremely acidic chemicals in special glands. For a long time, researchers believed that ants sprayed this poison, which consists mainly of formic acid, only to ward off other ants and possible predators. But Cremer and her colleagues showed in two studies the 2013 and in 2018 it appeared that ants use the acidic liquid to disinfect nestmates who are contaminated with pathogens. In the study, which has now been published in the journal "Current Biology", the scientists find a new benefit for formic acid: ants of the Lasius neglectus species use formic acid to clean their nest prophylactically, presumably to ensure that the nest is clean before first occupation.

Chemical weapon and cleaning agent

But since ants also use their poison as a chemical weapon, its use in the nest raises further questions, as Cremer explains: "How can ants spray this aggressive acid in their nest and fog their sensitive brood with it?" Because while a thick skin, the cuticle, the adult ants and a hard shell, the chorion, protect the eggs, the cuticle of pupae is thin and permeable. However, the Lasius neglectus dolls are wrapped in a silk cocoon, which the researchers believe could offer the dolls some protection.

The team searched for the answer through a series of experiments. First they removed the protective silk cocoons from some dolls and found that these naked dolls survived just as well on their own as dolls wrapped in cocoons. But if they put the naked dolls and workers in a nest together, more naked dolls died than wrapped dolls. Is the increased death caused by formic acid? To test this, the researchers taped the workers' poison glands shut with superglue.

Protective cover for the little ones

"We created a 'functional knock-out' by creating animals that cannot spray formic acid," explains Cremer. In a nest with workers who can no longer spray formic acid, naked and wrapped dolls had the same chance of survival. "So it is formic acid that kills naked dolls, and from which the dolls in the cocoon are protected," Cremer concludes - and we behave similarly: "When cleaning with aggressive agents, we also use gloves to protect ourselves. The cocoon has thus a similar function to protective gloves. "

The study provides the first example at the colony level of so-called immunopathology, a phenomenon also known from the human immune system. The immune system often fights pathogens with toxic substances, at the same time it has to keep the damage to its own body cells as low as possible. The immune system is faced with the crux of fighting pathogens as aggressively as possible and protecting the body's own cells and organs from collateral damage. Something similar happens with ants at the colony level: They protect the most sensitive parts of their colony from the harmful side effects of cleaning with their aggressive poison.

Mystery of missing cocoons

The study could also provide an explanation for why some ant species lost their original cocoons and other species retained their original cocoon, explains Christopher Pull: "Building a cocoon is associated with costs for ants, for example it can lead to a longer development time for the pupae. It is not yet clear why some ant species have a cocoon while others have lost it. Here we show that the cocoon protects ants in a sensitive phase of their development. It remains to be clarified whether ant species without a cocoon clean their nests with less aggressive chemicals. " (red, October 9, 2018)