Ants Swallow Acidic Butt Juice to Protect Themselves From Germs, Says Study

Ants wash down food or water with their own butt acid to cleanse their glands and protect themselves from germs, according to a recent study published in the journal eLife.

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Ants swallow their own butt acid to protect themselves from germs

"The behavior didn't seem to be linked to digestion, because ants do this even after they have only ingested water," said Simon Tragust, a zoologist of the Martin Luther University in Germany, according to a blog post.

To solve the mystery of this extremely antisocial behavior, Tragust and colleagues took steps to prevent the ants from reaching their rear ends. To begin, they let Florida carpenter ants (Camponotus floridanus) feed first, but then immobilized them with ice — the cold temperature of which causes them to stop moving without permanent damage) — and tested the pH levels of the ants' digestive systems.

The ants' acidic levels fell when they were unable to ingest the poisonous substance called formic acid that comes from a gland called an acidopore in the creatures' abdomens, reports Science Alert.

Acidic butt juice improves ant immunity to pathogens

Carpenter ants make use of formic acid to disable their prey, smearing their victims with the chemical after biting it with powerful mandibles. Formic acid is best known as a weapon ants use against predators — in fact, some species (like wood ants) hurl the poison at the faces of their enemies, like pint-sized monkeys gone wild.

However, some birds take advantage of this behavior — provoking ants to spray them with it to rid themselves of bird-borne pests. Humans, too, use formic acid as an antibacterial agent in livestock feed — in pesticides, wart removal procedures, and we've even secured a role for the acid in possible future energy technologies.

Just like us, ants have also found several applications for their butt juice — including as a chemical disinfectant. The ants use formic acid to sterilize their nests and clean their babies, which keeps the spread of harmful fungi at manageable levels. The new study also shows us how the ants use butt acid to keep their insides free of pesky parasites.

"We found that access to the poison improved survival of formicine ants after feeding on pathogen contaminated food," wrote the team in their paper.

Ants have strangely low microbial diversity

When humans come into contact with a high dose of formic acid, it can cause corrosive burns to our tissues, generating headaches or confusion when inhaled. And if anyone decides to make like an ant and swallow the butt juice, it can cause bloody vomiting.

Ants can take it, though.

The ants also have surprisingly low levels of microbial diversity in the microbiome of their guts. Beyond the obvious reasons, this is weird because they share food with one another, and spend a lot of their time in groups — everyone now knows this as a perfect way to spread dangerous pathogens — while they move through tunnels of dirt or rotting wood (which is also a great place for microorganisms to flourish).

Ingesting formic acid into their own digestive system might explain this.

Butt acid used to sanitize food for young

However, the butt acid let one bacteria slip by a hot death — Acetobacteraceae — which could withstand and thrive within a medium filled with formic acid during lab tests. But the pathogenic microbe species the research team tested did not.

The research team explained this resilient bacterium is also found in many other ant species, with recent studies suggesting it might be useful to ants — perhaps serving to assist ants' digestion of necessary nutrients.

"Acid swallowing acts as a filter mechanism, structuring the ant's microbiome," said Tragust in the Martin Luther blog post.

While stomachs with high acidity are common in animals with backbones (which includes us humans) — it's rarely observed in insects. How they maintain a low pH level is at present beyond our knowledge. But sanitizing food via antimicrobial methods is especially present in animals providing food for their young — like ants.

How ants maintain low pH level remains unknown

Tragust and the research team discovered ants lacking access to their acidic butt poison exhibited varying acid levels in their crop — a stomach-adjacent area that holds food meant to be shared with the wider colony — which might mean they possess additional ways of increasing the acid levels inside their digestive system.

It could be internal — our own stomachs secrete acids — but further investigation is needed to know for sure.

"The results of our study show that formicine ants maintain a highly acidic baseline pH in their stomach, the crop, through swallowing of their poison gland secretion during acidopore grooming," explained Tragust and the team.

While humans often have to resort to labs, pharmacies, and chemical industrial infrastructures to cleanse our food and bodies of pesky germs, ants simply wrap their mandibles around their rear end and swallow acidic butt juice — which regulates their internal biodome. Many likely find this news beyond interesting, but most of us are probably grateful that in this case, humans have found other ways to cope with bacteria.