ANTS THAT MAKE MILK, EXPLODE AND FORM ARMIES

ANCIENT SPECIES OF ANT

Nothomyrmecia macrops workers,

“Nothomyrmecia macrops” is a species of ant that is virtually identical to ant species that roamed the earth 100 million years ago. These ants form only small colonies with about 80 individuals, compared to other species with form colonies with hundreds of thousands of members, and forage at night when other insects, sluggish from the near freezing cold, are easy prey.

Up until the late 1970s only two specimens of these "holy grails of the ant world" had been found and they were collected by the niece of amateur naturalist on a summer outing at remote Cape Arid in Western Australia. In 1977 entomologist Robert was traveling to this cape to look for specimens when his car developed brake trouble several hundred miles before his destination. While the brakes were being fixed he wandered into the bush to relieve himself to his surprise he found a colony of “ Nothomyrmecia macrops” . Since his famous leak 70 other colonies have been found in an area called Poochera.

Army Ants

Army ants are found mostly in the tropical rain forests of Asia, Africa, Australia and the Americas. There are 320 known species of them with 150 in the New World, mostly in tropical areas of Central America and northern South America. In Africa they are called drivers. In South America they can form armies three quarters of million strong. Army ants in the Old World and the New World are thought to have independently evolved the same lifestyle and method of hunting. [Source: Mark W. Moffet, National Geographic, August 2006]

Unlike most other ant species, army ants don't form permanent colonies. Instead the roam across the forest floor in armies with several hundred thousand individuals that cover the earth like a living layer of soil, reaching for prey. A typical colony of an army ant species is comprised of five kinds of ants: the queen and four sizes of workers — minors, media, submajors and majors — which live only a few months. The three smallest workers kill and carry prey, feed the queen’s larva an maintain trails. The majors, or soldiers defend the colony.

The soldiers often have huge, sharp, hook-like jaws. Clumsy at anything but intimidating and fighting, they patrol the edge of trails and confront anything that seems threatening. Soldiers that put to up fights essentially commit themselves to suicide mission because once they sink their jaws into something the hook like designs of their jaws prevents them from being extracted. Many species use the jaws to gain a firm grip and then deliver a nasty, poisonous sting from their abdomen. Amazon tribes have traditionally used soldier ant as sutures, letting the ants bite into a wound and cutting off the body and leaving the heads in place.

Army Ant Bivoacs

army ant bivoac

Instead of forming permanent nests in trees or in the ground, army ants form temporary nests called bivoucs made up of masses of ants linked together like trapeze artists underneath a log or woody overhang or some other objects. The interlocked ants form balls that be two or three feet in diameter, complete with passageways formed by individual ants. At the center of the ball is the queen.

A bivouac is an organic structure formed by migratory driver ant and army ant colonies, such as the species Eciton burchellii. A nest is constructed out of the living ant workers' own bodies to protect the queen and larvae, and is later deconstructed as the ants move on

Describing an army ant ball, David Attenborough wrote: "The outside surface is formed by a lacy sheet of soldiers, their legs linked together, their huge jaws agape, ready to slice into anything that might interfere with them. Within the mass, the smaller workers have in a similar fashion created chambers in which the pupae hang. And at the heart of the community sits the queen. She is almost an inch long, twice he length of any other individuals in her army. Her body glistens with a special polish for she is continually groomed by her servants.

A colony typical establishes a bivouac at a site for about 20 days. During that time the queen works overtime to produce eggs and may lay as many as 300,000 eggs while workers conduct raids in a different direction every day to make sure they don’t cover the same territory twice. When the eggs have hatched into pupae and pupae have become workers, and food sources have been depleted the army moves on.

Army Ants on the Move

Army ant colonies alternate between periods of living in bivouacs and periods when they are on the march. Their When they are on the move the ants cover 100 meters a day for two weeks to a month, move, raiding as they go and bivouacking along the way each night.

Army ants march in columns that may take several hours to pass a single spot. At the front are soldiers who scout for food. Behind them are workers, a dozen or so abreast, many carrying larvae. When the column stops soldiers race to the flanks, offering protection with the huge jaws.

When obstacles are reached they form ladders for other climb. They also construct canopies for protection from damaging sunshine. When army ants reach a depression they quickly build bridges so they cab keep moving as quickly as possible. Dr. Iain Couzin, a mathematical biologist at Oxford University, told the New York Times, “They build the bridge with their living bodies. They build them up if they’re required, and they dissolve them if they’re not being used.”

The column, which may contain hundreds of thousands of individuals, marches day after day. The larvae produce pheromones which keep the ants on the move. If rival army ant species meet by chnace they sometimes go to war. The battles featuring intimidating and sparing but generally end within an hour with a retreat and without any deaths.

Feeding Army Ants

Army ants form attack in formations called swarms that may consist of several hundred thousand ants and expand outward like a fan to a width of 15 meters. In some places specialized birds follow the swarm preying on insects that try to flee. If the soldier scouts locate any prey they swam all over it and cut it into pieces. On trails between the hunting sites and a bivouac, workers carrying prey travel down the center while outgoing ants travel on the sides.

Describing army ants on the hunt, David Attenborough wrote: "If they discover a grasshopper or beetle, they swarm all over it, sinking their jaws between the joints of its external skeleton and dismember it with surgical precision. The fragments may be eaten there and then or tucked away beside the column to be collected when the hunt is over and taken back to feed the queen and those who stayed back in the camp to tend and protect her."

Submajors carry the large pieces back to the bivouac, assisted by media workers whose job it is to make sure pieces don’t touch the ground. Often minors act as “living roadfill,” filling up pot holes to even out the path used by workers carrying prey. The workers that do the killing are often sprayed with blood-like hemolymph by their prey and are cleaned off by other workers when they return to the camp.

Army ants generally feed on spiders, roaches, grasshoppers, beetles and other ants. They will kill but generally not eat anything that gets in their way’scorpions, tarantulas, lizards, frogs and even small snakes. There are stories of creatures as large as dogs, horses, cattle, people and pythons being killed by army ants. In some parts of Africa tied up or penned up animals are sometimes killed by the painful, toxic bites of army ant swarms. The only way to deflect their onslaught is pour paraffin in the ground and set it on fire.

Mark W. Moffet wrote in National Geographic: “Armored tough, with machete jaws, these masterful fighters hack and dice prey vastly large than themselves by acting in numbers beyond easy comprehension...Being blind, they can’t see what’s ahead of them, but moving in such numbers they overwhelm their prey.”

Ants That Make Milk

In a paper published in December 2022 in Nature, a team of scientists led by Daniel Kronauer of Rockefeller University in New York said that ant pupae provide an important service to the colony: Their developing bodies make a milk-like substance that provides important nutrients to the rest of the colony. This trait doesn’t just exist in one species; it is found in at least one species in each of five major ant subfamilies, suggesting that milky excretions could be common in a number of ant species. “I was surprised,” says Susanne Foitzik of the University of Mainz in Germany, who was not involved in the study, “as I did not see this before, despite watching ants for three decades. I am really curious and will start my own observations as soon as possible.” [Source: Tim Vernimmen, National Geographic, December 1, 2022]

According to National Geographic: The intriguing liquid was discovered by Orli Snir, a postdoctoral fellow who had not worked with ants before she joined the Kronauer lab. With fresh eyes, she quickly noticed behaviors that didn’t seem to be explained by the existing scientific literature. But he did agree when Snir proposed an unusual experiment. Instead of trying to make sense of the combined activity within the colony, where pupae and larvae are constantly being groomed, moved around or even piled together, she decided to watch the pupae in isolation. It took time to figure out how to keep them alive, but eventually, she found the right temperature and humidity level. Then, something really weird happened: the pupae were producing a liquid, and lots of it.

So much, in fact, that many were drowning in it, says Snir, at least if they didn’t die from a fungal infection first. Was this an abnormal phenomenon due to the pupae’s isolation from the colony, or something entirely normal that had gone unnoticed until now? To find out, Snir injected blue food dye into the opening where the fluid was coming from and put the bluish pupae back in the colony. (Read how ants led paleontologists to discover 10 new species of ancient mammals).

Soon enough, she noticed adult ants removing the liquid from the pupae and swallowing it, as revealed by the blue color spreading through their guts. They also often deposited young larvae on the pupae, which were also feeding on the liquid; they turned blue as well.

The finding has surprised and delighted the worldwide community of myrmecologists. “This is a very solid and well-designed study,” says myrmecologist Laurent Keller of the University of Lausanne in Switzerland, who agrees the phenomenon may be quite common. Bert Hölldobler of Arizona State University, who has studied ants since the 1960s, says he once suspected there might be something about the pupae that attracts adults. “I never picked up this topic again,” he says, “although it remained in my mind. I am absolutely delighted these researchers did.”

A chemical analysis of the liquid revealed that, besides other waste products from the metamorphosis, it contains all essential amino acids, as well as multiple carbohydrates and some vitamins. Pupae in other insect species tend to reabsorb and recycle these nutritious liquids, says Kronauer. The sharing of nutrients among different life stages in ants may be at the root of the intensely social lifestyle that these insects have evolved over millions of years, Kronauer and Snir suggest. “This makes ants in different life stages depend on each other,” says Kronauer. “It’s a kind of social glue that keeps them together.”

Adria Le Boeuf, a myrmecologist at the University of Fribourg in Switzerland studying the exchange of nutritious substances between ant larvae and adults, agrees. She adds that they may have paved the way to the more complex behaviors she is investigating. “This fluid may have aided the evolution of [the ants’] cooperative brood care, as it incentivized adults to care for the young. And once ants started drinking this, that may have set the stage for the transfer of other things.” Are a few sips of pupal fluid really the root of ants’ ever-expanding sharing economy? Digging deeper in future research is likely to yield ever more discoveries of one of the planet’s most widely studied and yet still very mysterious groups of insects.

Ants That Perform Leg Amputations and Know When They’re Needed

In July 2024, in a study published in Current Biology, scientists announced that had found an ant species that can amputate each other's legs and can also determine whether it was needed depending on the location of the wound. It was the first observation of a non-human species of performing purposeful surgery. [Source: Jennifer Vilcarino, ABC News, July 4, 2024]

Jennifer Vilcarino of ABC News wrote: Ants are territorial and can get into rough encounters with rival colonies which can lead to injuries, according to scientists. But Florida carpenter ants — also known as Camponotus floridanus — have adopted an effective wound treatment: amputation. The process of amputation takes about 40 minutes and requires one ant to chew on its nestmate's affected leg, according to Laurent Keller, one of the researchers in the study. "They go to the upper parts [of the ant's leg and] the mandibula will cut it," Keller told ABC News. "The other ant will clean the new wound."

After a researcher reported his observation of amputation to other researchers in a lab in Switzerland, they noticed that the carpenter ants selectively conducted amputations. If an injury was near the femur rather than the tibia, ants would amputate. Researchers were interested in the decision process behind amputation and performed micro-CT scans on the amputated ants, according to the study.

The researchers hypothesized that the closer the injured muscle was to the body the more likely the surgery would occur. "We had a hypothesis that maybe the injury level of a tibia had an infection that evolved too quickly for ants to cut the leg to prevent infection," stated Keller. According to the study, the ant's femur is primarily responsible for leg hemolymph circulation, similar to a human's blood flow, and therefore cutting it off slows the rate of an infection spreading and allows for sufficient time to perform an amputation.

Ants that had a tibia injury weren't left for dead. Instead, they received wound care, the researchers said. Keller noted that there hasn't been any research on how an ant cleans a wound. "We have not studied how they do it really, but we figure that mandibula must be really clean when they do," stated Keller. The study in Current Biology builds on previous research that shows how termite-hunting ants have metapleural glands that allow them to produce an antimicrobial compound to treat affected wounds. However, carpenter ants, amongst other communities, have lost this ability due to evolution.

Ants That Explode to Protect Their Nests

Veronique Greenwood wrote in the New York Times: “Outside the kitchen door at the Kuala Belalong Field Studies Center in Brunei, on a number of trees near the balcony, there is a nest of very special ants. They explode. This colony was studied in depth by scientists who, April 2018 in the journal ZooKeys, published an in-depth description of the newly named species, called Colobopsis explodens, including a portion of their genome sequence. “Workers of C. explodens have a distinctive, rather foul talent. When their nest is invaded, they rupture their own abdomens, releasing a sticky, bright yellow fluid laced with toxins on their attackers. Similar to honey bees that die after stinging, the exploded ants do not survive, but their sacrifice can help save the colony. [Source:Veronique Greenwood, New York Times, April 23, 2018]

“Exploding ants have been known to science for more than 200 years, and the special ability for which they are named was first documented in 1916. But since 1935, no new species from the group had been officially named and described. To do this, ideally one needs to collect members of all the different castes in the colony, from worker to queen, write a detailed description of their appearance, and give the species a Latin name, among other things, said Alice Laciny, a graduate student at the Natural History Museum Vienna who is an author of the new paper. “We knew they existed, and we did experiments on them,” she said, “but it wasn’t described as an official species yet.”

“Ms. Laciny is a member of an eclectic group of researchers who are united by their fascination with these insects and who describe in the new paper how C. explodens live and spectacularly die. At 6 a.m., the ants come out of their nest and forage for food until about 6 p.m., the researchers found, although it is not exactly clear yet what they eat. A small squad of workers often stands at the entrances of the colony and touches every ant that comes in or out, apparently monitoring the movements of their sisters. The researchers also introduced a weaver ant, a natural predator of exploding ants, to observe the workers’ explosive response.

“A C. explodens worker ant. Exploding ants have been known to scientists for more than 200 years, but only recently have been officially described.Credit...Heinz Wiesbauer When a predator touches a worker, the worker will often rupture, tangling the predator in a gluey mess and eventually poisoning it. This strategy of voluntary self-sacrifice makes evolutionary sense because the ants of the colony are all closely related, and the workers are sterile. “Their way of taking care of their own genes is to sacrifice themselves so the rest of the colony can survive,” Ms. Laciny said.

“During their research, the team realized that several elusive males, which have wings and are very rarely seen, were emerging from the nest and flying off into the rain forest. Males of exploding ant species are difficult to distinguish from each other, Ms. Laciny said. Glimpsing them as they left their own nest was a stroke of luck, and she and a colleague ran after the newly fledged males, dodging through the trees and catching a few in glass vials, which became part of the reference collection of C. explodens described in the paper.

Image Sources: Wikimedia Commons

Text Sources: Mostly National Geographic articles. Also David Attenborough books, Live Science, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, and various books and other publications.

Last updated December 2024