The antimicrobial compounds ants excrete to defend themselves from pathogens may protect plants as well.

by Emily Makowski

Some ants produce natural antibiotic chemicals to defend themselves against fungi and bacteria. Ecologist Joachim Offenberg of Aarhus University in Denmark wondered what effect these compounds had on the health of the plants the ants called home. “We had this thought that if ants produce antibiotics, maybe these antibiotics could have an effect . . . on the diseases of the plants they walk on,” he tells The Scientist.

In a review of studies investigating the effect of ants on plant pathogens, he and fellow Aarhus ecologist Christian Damgaard found that, out of 30 plant species that were commonly inhabited by some kind of ant, 18 showed a decrease in the effects of pathogens. These included reduced bacterial load and increased germination rates enjoyed by plants inhabited by ants compared with plants of the same species that did not host ants.

Data have long confirmed that ants provide protection to their botanical hosts by eating pests, says Andreas Schramm, a microbiologist at Aarhus University who was not involved with the study. “The chemical defense of plants is really another direction that the authors quite convincingly put out here,” he says. Overall, Offenberg and Damgaard estimated that the effects of ants’ antibiotics were comparable to the benefits plants receive from the insects’ consumption of herbivorous pests.

Six of the plant species had increased pathogen incidence with ants, however, and six either had no significant difference between groups or insufficient data. Offenberg notes that a plant that hosts ants may already have a major infection that can’t be controlled with ant-produced antimicrobial compounds. Moreover, the insects can inadvertently disperse pathogens: fungal spores, for example, can cling to their legs.

Ants Stick to Cliques to Dodge Disease

By Lucy Huang

Ants infected with fungal pathogens steer clear of other cliques within the colony—avoiding wider infection, and allowing for a sort of immunity. Lucy Huang reports.

It’s peak cold and flu season, which means taking a lot of preventive measures. Frequent hand-washing is a must. As is avoiding co-workers or friends who are sick. But we humans are not the only animals that change behavior to keep diseases at bay. So do ants.

“So there are the foragers and the nurses– it’s two different groups of work.”

Nathalie Stroeymeyt of the University of Lausanne. She and colleagues observed ants to see their reaction to the presence of a pathogen.

“With the nurses staying inside the nurse taking care of the brood and being made of young workers. And the foragers are all the workers at outside of the nest to collect food and defend the territory.”

Forager ants are at greater risk of getting exposed to diseases because they leave the safety of the nest. So the researchers sprayed a common fungus on a small group of forager ants and then followed their movements to see the way other ants reacted.

“We marked all ants in the colony was individual labels, which carries these two-dimensional bar code marks like QR code which is automatically detected and recorded using a tracking system.”

After the infection, the nurse and forager ants stayed within their cliques and interacted less outside of their work group. The researchers also saw that forager ants spent more time outside of the nest.

“They increase that amount by 15 percent so by quite a long large amount.”

The researchers also measured the amount of fungus on each ant and saw that it was almost completely contained within the foragers group. Some nurse ants and even the Queen did have trace amounts of the fungus’ spores on them but the amount was small enough that they could easily groom them off of their bodies. The study is in the journal Science. [Nathalie Stroeymeyt et al., Social network plasticity decreases disease transmission in a eusocial insect]

Not only does the cliquish behavior stop the spread of the fungus, “but it allows you to develop immunization. Something that’s quite interesting in these ants that’s been shown by other study is that when you receive very small amount of these spores, you don’t have an increase in mortality risk because it’s low enough that you can heal, it’s sort of boost your immune defenses and protect you against later exposure to the same pathogen.

Seems that in their ability to avoid infecting other members of the community, ants may be more advanced than we are.

Exploding Ants Kill Foes, and Themselves, with a Blast of Toxic Goo

By Mindy Weisberger

Treetop-dwelling ants from Southeast Asia have an explosive defensive move: The insects take down their foes by blowing themselves up. If that sounds gut-wrenching to you, just imagine what it feels like to the ant.

Commonly known as “exploding ants,” workers in this group respond to threats by deliberately (and fatally) rupturing their body walls, spattering rivals with toxic fluid.

Exploding ants are typically lumped together into a species group called Colobopsis cylindrical, but researchers recently determined that there are at least 15 species of these self-sacrificing insects — including one previously unknown species in Borneo, which they described in a new study.

Many animals engage in chemical warfare, stewing toxic brews in their own bodies to subdue prey or scare off enemies. Venomous creatures — which include snakes, spiders, insects, fish, cephalopods, amphibians, reptiles and even some types of mammals — deliver their toxins with stings, stabs or bites.

But others, such as skunks, venom-squirting scorpions and bombardier beetles, opt to spray their chemicals. In fact, bombardier beetles can emit their heated, poisonous blasts even after they’ve been swallowed, with unfortunate results for their predator’s digestion (and a sticky escape for the beetle).

However, defensively rupturing one’s own body — a process called autothysis, from the Greek words for “self” and “sacrifice” — is somewhat more unusual, and is known only in ants and termites, the scientists reported.

Tick, tick, boom!
The new ant species — Colobopsis explodens — was formerly called “yellow goo,” after the brightly colored gunk produced by its exploding worker ants. Their colonies can contain thousands of individuals, inhabiting the leafy canopies of trees that stand as tall as 197 feet (60 meters), and covering an area of at least 26,900 square feet (2,500 square meters), the study authors reported.

The researchers decided to make C. explodens a model species — one that scientists look at to draw conclusions about a larger group; in this case, exploding ants. They noted that C. explodens ants were “particularly prone to self-sacrifice” in the presence of threats — which included intruding researchers.

To blow themselves up, the reddish-brown minor workers — all sterile females — contracted a part of their abdomens called the gaster. They clenched it so tightly that it ruptured, spewing a yellow secretion that was manufactured in the ants’ jaw glands and had “a distinctive spice-like odor,” according to the study.

And suicidal explosions aren’t the only weird adaptation in C. explodens. Major workers — the bigger “soldier” ants that are also sterile females — have enlarged heads with raised shield-like sections that are circular and flattened at the top. The oddly shaped heads create a perfect plug that the ants use to temporarily block openings into their nests, the scientists wrote.

The findings were published online today (April 19) in the journal ZooKeys.

Original article on Live Science.

Fijian ants grow their own plant cities and farm tropical fruits

By Alice Klein

Ants beat us to it. A Fijian ant first started planting fruit crops 3 million years ago, long before human agriculture evolved.

The ant – Philidris nagasau – grows and harvests Squamellaria fruit plants that grow on the branches of various trees.

First, the ants insert seeds of the fruit plant in the cracks in tree bark. Workers constantly patrol the planting sites and fertilise the seedlings, probably with their faeces.

As the plants grow, they form large, round hollow structures at their base called domatia that the ants live in instead of building nests. When the fruit appears, the ants eat the flesh and collect the seeds for future farming.

Guillaume Chomicki at the University of Munich, Germany, and his colleagues discovered that each ant colony farmed dozens of Squamellaria plants at the same time, with trails linking each thriving hub. The connected plant cities often spanned several adjacent trees.

The researchers found that Squamellaria plants are completely dependent on the ants to plant and fertilise their seeds. At the same time, Philidris nagasau ants cannot survive without the food and shelter provided by the plants. The Fijian phenomenon is the first documented example of ants farming plants in a mutually dependent relationship.

Trees in nearby Australia have been observed with similar-looking ant-filled plants growing along their branches, but no one has known why, says Simon Robson at James Cook University in Australia. The plants are from the same family as Squamellaria, suggesting they have the same symbiotic farming relationship with ants.

Chomicki’s team also conducted a genetic analysis to study the history of the Fijian ant-plant interactions. The results showed that the ants lost their ability to build nests around 3 million years ago, at the same time as the plants developed roots that could grow in bark. This signals the beginning of the mutual relationship, which emerged when Fiji and Australia were still connected.

Brainy ants
Only a handful of other species have been found to farm their food. For example, Yeti crabs cultivate bacteria on their claws and sloths grow algae gardens on their fur. Ants have been known to cultivate fungi, but this is the first time they have been found to plant crops in such a mutualistic manner.

The fact that ants have developed such sophisticated food production skills confirms the impressive teamwork of ants, says Kirsti Abbott at the University of New England, Australia.

“Ants are a lot smarter than we think they are – we call them superorganisms because they form networks that are much like our brains,” she says. “The information flow among ant colonies is just insane compared to human social systems, so this finding does not surprise me in the slightest.”

Journal reference: Nature Plants, DOI: 10.1038/nplants.2016.181

Ants trapped in nuclear bunker are developing a new form of ant society


By Richa Malhotra

Keep calm and carry on building. That’s the motto of 100,000 or so wood ants stranded without food in a nuclear bunker until they starve.

Wood ants (Formica polyctena) typically build a cosy mound nest on the forest floor. They seek out the sugary secretions of aphids living on trees and supplement their diet with insects. Now, scientists have uncovered a population of wood ants that has sustained for years without food and light inside a bunker where temperatures are constantly low.

The ant population was discovered in 2013 by a group of volunteers counting bats overwintering in the bunker, which is part of an abandoned Soviet nuclear base near Templewo in western Poland.

Later, Wojciech Czechowski at the Museum and Institute of Zoology in Warsaw, Poland, and his colleagues, entered the bunker to study the ants more closely. They noticed that the wood ants had built a nest on the terracotta floor of the bunker – right below a ventilation pipe. Looking up through the five-metre-long pipe, they realised where the bunker ants come from.

A 60-centimetre-high wood ant nest sits on the forest floor directly on top of the ventilation pipe outlet. But because the metal cap over the ventilation pipe has rusted, ants can fall through from time to time.

It’s a one-way journey for any ant that falls into the bunker. They can scale its 2.3-metre-high walls but Czechowski and his colleagues realised that – for some reason – the ants never walk across the bunker ceiling and so are unable to reach the ventilation pipe to make it back home.

So, how did they respond? “These ants gathered together and did what ants do,” says Terry McGlynn, an entomologist at the California State University Dominguez Hills, who was not involved in the study. “They built a nest and eked out an existence.”

Today that nest covers most of the floor of a chamber that measures three metres by one metre.

Czechowski and his colleagues have looked for evidence of a food source that the bunker ants could use, but haven’t found one yet. Rather, the ants seemed to be doomed to starve to death in pitch-blackness. They found ant corpses carpeting the bunker floor in layers a few centimetres thick and estimated the number of dead ants to be about two million.

Without any food, the individual bunker ants are probably dying at a rate faster than at the surface, the researchers think. But because there is a steady stream of new arrivals falling into the bunker, the colony has grown to a reasonable size.

This explains one of the unusual features of this nest. When the researchers dug into it to look for an ant brood they found none – no larvae, pupae or empty cocoons. The “colony” was queenless and lacked any males. This fits with the idea that it is no ordinary nest, but a strange nest-like structure that the worker population has instinctively built.

“This is kind of fascinating that such a huge non-productive nest could exist on its own, built solely from the ants that got trapped in the bunker,” McGlynn says.

Journal reference: Journal of Hymenoptera Research, DOI: 10.3897/jhr.51.9096