Follow up to the previous post!
This was an assignment for a capstone course I took on science communication, so I’ve included the hard-formatted “magazine-style” version below, but you can also read the article in plain text below.
Enjoy as we delve into the world of ants and infection!
Little Brains, Big Ideas
Insects often seem to defy the laws of nature — cockroaches might outlive us in the case of a nuclear apocalypse and it was once thought that bees violated the laws of physics by flying. We never expect such small creatures to be able to perform extraordinary feats. No insect exemplifies this better than the noble ant and its extraordinary intelligence.
Although they have tiny brains compared to us, social ants have some of the largest brains in the insect world. And in many respects, they are just as advanced as us big-brained humans, if not more so. They optimize paths to and from food sources, communicate within a massive network of organisms, cultivate crops, and herd livestock like tiny farmers. They even have a kind of healthcare system! In fact, some of their most amazing feats have to do with disease and infection.
Ants often become infected by Metarhizium brunneum, a highly contagious fungus that has even been tested as a pesticide due to its efficiency at killing insects. While it’s different than the zombie ant fungus you’ve probably heard about, the outcome is the same: dead ants. What’s really interesting isn’t the fungus, but how ants behave when someone in the colony is infected.
Are sick ants smarter than sick humans?
Grooming
It’s relatively normal for us to use (or at least be asked to use) hand sanitizer when we enter a busy place like a hospital in order to prevent sickness from spreading. This behaviour is the product of thousands of years of research into illness and infectious disease, then even more working to develop medicine to prevent infections. So what would you say if I told you that ants have been using hand sanitizer for even longer than we have?
It’s not quite hand sanitizer, but, with the help of evolution, ants have developed a disinfectant as well. Made mostly of formic acid, they make this solution in their own bodies and use it for lots of different things: making their bites more deadly, breaking down food, or even shooting it at their enemies from afar. The most advanced use is, of course, as a sort of medicine to kill the spores of dangerous fungi.
When ants have been exposed to M. brunneum, other ants will try to both physically remove spores with their antennae as well as using the formic acid to kill anything that remains. Studies have shown that both methods are very helpful, so helpful that the cleaners will hurt themselves in order to effectively clean their nestmates! While some ants will shoot the disinfectant onto nestmates directly from their acidopores, holes at the end of the abdomen, others will actually suck acid up from the acidopores and then apply it to nestmates from their mouths. Having acid in the mouth is painful for the ants and might do a little damage, but it allows them to more evenly spread the disinfectant and keep waste to a minimum. If it means they don’t later get infected and die, the painful application method is definitely worth it.
Grooming after pathogen exposure, known as allogrooming, can include nestmates as well as brood — the immobile ant eggs and pupae that are cared for by the workers. Brood with shells or cocoons are somewhat protected from infection, but deadly spores can still make it through, and use their bodies to spread the infection to others. Pupae can’t really act any different while infected since their actions wholey consist of sitting in a pile of other pupae, nor can they communicate to tell anyone that they’re sick. This is why it was surprising to scientists that the caretakers could identify sick brood with an accuracy rate of 95%. That’s more accurate than modern flu tests! The workers actually identify sick eggs and pupae through smell: when the brood fall sick, the chemicals that normally coat their bodies change, making them smell differently. Since ants can communicate a lot with these smells (which nest they are from, if they are a worker or a queen, etc), it’s no wonder that their sense of smell evolved to be used to sniff out sickness as well.
Once they’ve identified infected younglings, some ant species will simply carry them out of the nest and dump them outside so that they can’t go on to infect others in the nest. This is a bit of a cruel fate, especially for a baby, but there are some species that take things even a step further… Though harmless when applied on the exoskeleton, the formic acid disinfectant that ants produce is deadly if it gets inside of an ant. By ripping apart the pupal cocoon, ants will inject pupae with this solution, killing them instead of merely disinfecting.
While some of these “solutions” to infection might seem gruesome to think about as humans, they’re quite clever when you set aside your morals: developing a sort of medicine from something previously used as a weapon, using multiple methods of disinfection (some lethal) to prevent the collapse of an entire colony. Ants work for the greater good, and while this might not always be the ideal solution for humans, it has certainly given ants a leg up in the animal kingdom.
This ant is carrying an egg. Is it infected and in need of disposal? Is he simply taking it out for a walk? Who knows — we may never know what goes on inside the brains of ants.
An ant carrying its egg, Kaptai National Park – Nobaiha Zaman – Wikimedia Commons (CC BYASA 4.0)
Death & Dying
Fortunately, even if an ant becomes infected, it will not spread the disease to its nestmates until it dies and the fungus grows over its body.
While there are workers who remove waste (including dead bodies) from the nest, most adult ants will plan ahead and take care of this themselves before they die. When an ant becomes infected, it will actually leave the nest on its own — going off to die alone in the tall grass somewhere once it succumbs to the fungus. In the ant’s eyes, the least it can do in its remaining time alive is to prevent anyone else from getting sick. That’s more than a lot of us might be able to say — in how many zombie movies does the side character say “No, I’m just a little tired” before they turn and try to eat their friends’ brains? Ants are certainly more intelligent — or maybe just more noble — than we think.
Whether it’s an infected ant wandering off to die alone or a worker ant disposing of a dead body and risking becoming infected themselves, the life of one worker is a small price to pay for the safety of the colony. But what about the life of a queen?
As a pillar of the colony, the queen displays an unusual, but very leader-like behaviour: she will not leave if she becomes infected. The phrase “The captain goes down with his ship,” applies to ants as well as sailors, be it in a much less dignified way. If a queen becomes infected, she’ll just keep laying eggs until she dies. In fact, some research has found that ant queens will actually increase their egg-laying speed if they realize they are sick. By doing so, they are doing as much good as they can for the nest in their remaining time. This is especially interesting considering that the same study found that reproductive workers (workers that lay eggs alongside the queen) did not do the same, acting instead as a regular worker would even though they had the capacity to continue egg-laying. It goes to show how important the queen is and how different she is from the workers.
On the other side of the spectrum, queens do have to drop to the level of the workers sometimes. In colonies with multiple queens, one queen dying of infection means that it’s time for one of the others to step up to challenge of dragging her out. Instead of workers removing the body, as they would with dead workers, a queen must do this task. So much for royal privilege, huh? This makes us wonder about what exactly the differences between workers and queens are. Not only are ants’ choices more complex than we might have expected, but their caste system is as well.
Nest Choice
Despite some of their quirks, or perhaps because of them, queens make good leaders. Some of their most unintuitive choices end up being incredibly clever, including during nest selection.
Ant preference in real estate is baffling. When they have to find a new home, they generally spring for nests that have the dead corpses of infected ants in them. They actively want to expose themselves to this dangerous fungus instead of moving into an empty nest! Haunted houses aren’t something that most of us would spend extra money on, but ants have their reasons.
Originally, researchers thought that ants made this choice because the fungus was able to trick them — smelling nice and luring them into the nest. However, fungi with this type of power are incredibly rare: as the fungi evolves to attract ants, ants will evolve to not be attracted.
Scientists have now proposed that while it’s probably a little bit dangerous for the ants to be around so many dead bodies of infected ants, it’s also smart. This is because another part of their healthcare systems is their own form of vaccines. By exposing themselves to these dead bodies deliberately, they can control the amount of spores they get on them and immunize the whole colony as they enter the new nest. This is known as social immunization. Having your entire colony (or at least most of it) immune to a deadly pathogen is incredibly helpful, and may be why ants seem to be drawn to these death-traps.
When we think of insects, we generally think of the words small, annoying, and stupid. Everyone has seen a fly bash its head against a window 20 times in an attempt to get outside. But, although small, insects are often a lot smarter than we think. The things that ants do, the choices they make, may seem unintuitive at first (killing their children, choosing to live in a death-trap), but they are actually incredibly smart and are why there are trillions of them on Earth.
Ants are smarter than we think, and we can prove that through their healthcare system. Humans are having a measles outbreak right now because a bunch of us won’t use rigorously-tested vaccines, while ants are just rubbing themselves up against the bodies of the fallen and trusting that it’s for the greater good. Maybe we could learn a thing or two from these guys.
Observing ants has provided us with insights about not only the spread of disease, but also about pest control, agriculture, extended communication networks, and even traffic jams. What else could we learn from them? Only time will tell.
Selected readings
Giehr, J., & Heinze, J. (2018). Queens stay, workers leave: caste-specific responses to fatal infections in an ant. BMC evolutionary biology, 18(1), 202.
Pontieri, L., Vojvodic, S., Graham, R., Pedersen, J. S., & Linksvayer, T. A. (2014). Ant colonies prefer infected over uninfected nest sites. PLoS One, 9(11), e111961.
Tragust, S., Mitteregger, B., Barone, V., Konrad, M., Ugelvig, L. V., & Cremer, S. (2013). Ants disinfect fungus-exposed brood by oral uptake and spread of their poison. Current Biology, 23(1), 76-82.