It was an ambitious project that, though it failed, would become part of the iconography of the decade. In September of 1991, the first long-term residents moved into Biosphere 2, a 3 acre vivarium, built to be an artificial, materially closed ecological system. Biosphere 1 being the earth. A Texas oil billionaire funded it to study how people might one day be able to manage a self-sustaining ecosystem for life on Mars. It proved to be a lot harden in practice than it has been on paper. The oxygen level would drop too low, the crew didn’t really know how to grow crops for food, pollinators soon died out, and then the ants moved in. Not just any ants, crazy ants. My name’s…
They go marching two by two, they’re the subject of two CGI movies from 1998, and a picnic wouldn’t be complete without them; today we’re talking about ants. This topic comes to you by popular demand, two social media comments and an email. That’s a new record. So thanks to Rachel, AProdigious, and Kate from Strange Animals podcast. We should really think about ants more often, considering how many of them there are. I’ve often enjoyed dropping the fact that the ant population is equal to the human population by weight. But is it true?
The claim comes from the 1994 book Journey to the Ants, by a Harvard University and a German biologist. They based their estimate on the estimate of a British entomologist, who calculated that the number of insects alive on earth at a given moment was one million trillion. If ants make up 1% of the insect world, that’s ten thousand trillion. According to the book, “Individual workers weigh on average between 1 to 5 mg, according to the species. When combined, all ants in the world taken together weigh about as much as all human beings.” That assumes you would need a million ants on one end of the seesaw to balance each person, which the authors pegged at 62kg/137lbs. With around 13,000 ant species worldwide, comes a lot of variety. They range from as small as less than 1mm long to over 50mm/2i — that’s the aptly named Titanomyrma gigantea, by the way — so weights vary too, but experts seem to agree the average weight of an ant is less than 10mg.
But even among experts, no one really knows how many ants there are in the world. A BBC documentary claims there are not 10,000 trillion ants but 100 trillion, though it still suggests the total weight of ants equals the total weight of humans. Even by the authors’ own math, their calculation is wrong. If we estimate that the 7.2 billion humans on the planet today weigh a combined 332 billion kg/366 million tons, and 10,000 trillion ants, weighing an average of 4mg each, we get only 40 billion kg/44 million tons, or about 9 lbs of human for every pound of ants. Even if we allow for the smaller human population, and slightly smaller humans, at the time they wrote their book, it’s still back-of-napkin math at best. One expert does say that the numbers might have been accurate at one point, probably around 250 years ago. “We must also remember that humans are getting fatter all the time. We’re not just increasing in population, we’re increasing in fatness, so I think we’ve left the ants behind.”
Another way to try to wrap your head around how many ants there are is to look at the biomass. One of my favorite weird history and animated rant YouTube channels, Sam O’Nella, compared the biomass of several animals and visualized them as spheres, like literal animal planets. For example, all the blue whales in the world, if you mushed them together like play-dog, would make a spheroid 140m/450ft across (blue whales are huge, but there aren’t many of them). In contrast, the chicken planet is more than twice that size, 330m/1100ft across (their small, but we’ve bred a *lot of them). The math was tricky enough, what with the trying to come up with a density for each animal, but he also found order-of-magnitude disparities in the estimates of ant populations. Taking the average of the estimates, the ant planet came to 420m/1400ft across, or nearly as tall as the Empire State Building, putting it between the biomass of horses and sheep. So if your four year old ever asks how many ants there are in the world, you can come back with the questions, “By weight or by mass?” Bonus fact: Sam estimated the closest animal biomass planet to humans is the planet of krill, which are barely 5cm/2in long.
Lie bees, life in an ant colony revolves around the queen, who starts life the same as any other larva, but is fed a special diet by the all-female workforce that turns her into an egg-laying machine. Male ants are pretty much just a sperm delivery service, dying after mating at about a week old while the queen can live for years, but what’s fascinating about them is that they have a mother, but no father. Rather than having an X and Y chromosome, an ant’s gender is determined by whether they have one or two copies of their genome. Female ants develop from fertilized eggs with two genome copies, one from their father and one from their mother. Male ants develop from *unfertilized eggs, so have no genome from a father. This means that male ants don’t have a father and cannot have sons, but they do have grandfathers and can have grandsons. Try using that to break the ice while you wait for the Zoom chat moderator to get their mic working.
We think of ant colonies as individual communities, self-contained and not interacting with other colonies, but sometimes neighboring colonies of the same species can link up to work cooperatively. There is a “supercolony” of millions of cooperating nests of billions of Argentine ants (Linepithema humile) that spans over 3,700 miles/6,000 km of European coastline from Italy to northwest Spain. And you thought the way they’d taken over that corner of your yard was impressive.
That’s not the only Argentine ant supercolony though. Not only do they have the world’s largest supercolonies in such far-flung places as Japan, California and Europe, those are actually all part of the same global mega-colony. Large and highly-adaptable, they are incredibly successful at driving off competition. No other ant can beat them in a straight fight…except one. Recent research indicates that another invasive species, the Asian needle ant (Pachycondyla chinensis), is taking territory away from the Argentine ant. This is the first time Argentine ants have been observed losing territory. So what is the needle ant doing that every other species failed to do? Scientists aren’t quite sure. They know that Argentine ants seem to avoid needle ants, but they don’t know why. Asian needle ants have an advantage over Argentines because they can tolerate cold weather better, giving them more of the year to build nests, mate, and eat other ants, as needle ants are wont to do. While at first blush, you’d think it was a good thing someone could take a bite out of the reigning champion Argentine ants, that comes at a price. Needle ants have a painful sting that can cause allergic reactions and you’re actually more likely to be allergic to an Asian needle ant sting than to honeybee sting. Bonus fact: more people in Australia are treated for anaphylaxis from the deceptively-cutely named jack jumper ants than are treated for bee allergies.
Ants have a major influence in ecosystems worldwide, dispersing seeds, pollinating plants and improving the quality of soil. The power to make a difference in one’s environment cuts both ways, though. Fire ants cause over $4 billion worth of damage in the US every year. That includes both crop damage, as well as veterinary and doctor bills from running afoul of their nest and being bitten and stung. Fire ants aren’t even native to North America. They were accidentally imported from South America around the 1930’s through the port of Mobile, Alabama; probably in soil used for ships’ ballasts, the weight in the bottom that helps them stay upright. They’ve been spreading ever since. Their introduction wasn’t the last time fire ants traveled by water. Their habitat, along the southern third of the country, overlaps with the areas prone to hurricanes and flooding map. When colonies are flooded out, the ants band together into a flat mass that floats until they reach high ground or bump into a tree they can climb. The raft carries all members of the colony including eggs, larvae, queens, winged ants, and workers, according to Texas A&M University. Rafts save the ants, but make a bad situation worse for humans trying to rescue people in floods. If they come into contact with boats, the raft will break up as the fire ants climb aboard and immediately start biting the hell out of anyone on board. Texas A&M warns, “It’s important to rub them off immediately – submerging them won’t work, as they’ll just cling to the skin. Even a high-pressure water spray might not remove them.” Everybody gangster till the ant raft floats towards you.
Ants do some pretty remarkable things to protect the colony. Take the ant whose name is also a spoiler for this paragraph, Colobopsis explodens. They make their homes in the tall canopies of trees in southeast Asia, which they defend with a move called autothysis, from the Greek words for “self” and “sacrifice.” The way they sacrifice themselves is something unique to only a few species of ants and termites–they blow themselves up. Formerly called “yellow goo,” after the brightly colored gunk that’s left over, exploding ants respond to threats by deliberately (and fatally) rupturing their body walls, spattering rivals with toxic fluid. Many animals engage in chemical warfare, from cobra venom to skunk spray to the heated poison shot out by the bombardier beetle, but these 15 or so species of ant are the only animals that have to kill themselves to use it. Researchers noted that C. explodens ants were “particularly prone to self-sacrifice” in the presence of threats, including humans trying to study them.
When another insect gets into the nest, C. explodens workers will bite onto it, then curve their body toward it as if they had a stinger. To blow themselves up, the workers contract part of their abdomens called the gaster so tightly that it ruptures, spewing forth a yellow glandular secretion, which kills either them stone dead with the toxicity or immobilized by the stickiness. Not all C. explodens go to such extremes for the great good. Some play more defense and less kamikaze offense. All they do is shut the door, and by door, I mean their head. It’s a tactic seen in a few other species, including two recently discovered in Africa. Prior to that, only a single example of door head ant had been found on the whole of the continent and even then scientists weren’t sure if they were looking at a specialized caste or a separate species. But what do I mean by door-head ant? Exactly how it sounds
The heads of Cephalotes ants are large and flat, like the world’s most conspicuous flat-top haircut. They’re the ideal shape for the tunnels left over by beetles boring through tree trunks that the ants want to live in. This real estate is in high demand; other ants and parasites like phorid flies, who lay their eggs in the ants, want to move in too, and they’re not interested in making an offer. Tunnels are hard to fight in, all narrow and cramped, and it limits the number of defenders who can reach the attackers. So, best they not get in at all. The door-heads might be camouflaged, hiding in plain sight, ready to spring into action. Depending on the species, pores on their heads secrete tangled fibres that resemble fungi, or they catch forest debris with small hairs that act like Velcro. Then, with their decorated heads in the openings, the nest is harder to find in the first place. The ants prefer this strategy to fighting since Cephalotes ants aren’t the most formidable combatants once their armoured walls are breached. The door-heads are devoted to their job. It’s not uncommon to see door-heads with evidence of being bitten by would-be intruders when the door-heads wouldn’t budge. One researcher confessed, “I tried to see if I could dislodge a soldier, if I could push it back.” His forceps punctured the ant’s head [womp womp] because it wouldn’t budge. In his defense, the same researcher was the one who noticed that when ants live in only one kind of hole, they can grow heads that fit perfectly.
Blocking entrances is just one of the talents of an ant with a head so big, they’re called big-headed ants. One species, Pheidole megacephala (side-note: one of the 5 ants on the top 100 worst invasive species list) also use their bloody big heads to grind seeds and smash up other ants. The size of their head actually corresponds to the severity of the local competition. They grow heads three times larger in survival-challenging Australia, compared to their easy-living cousins in Hawaii. They also have a unique rank in their caste system, so rare that only 8 of the 1100 known Pheidole species have it. After minor and major, they have supermajor. The minors are workers, the majors are the soldiers with big heads, and the supermajors have even more massive heads. Scientists believe the capacity to create supermajors is a throwback mechanism dating back to their prehistoric ancestors 35–60 million years ago.
Speaking of dinosaur times, have you ever seen a dinosaur ant? Now would that be an ant the size of a dinosaur or a regular-sized ant with vaguely thunder lizard proportions? It’s the old Venture Brothers ghost pirate/pirate ghost semantics. Sadly, it’s neither of those things. Dinoponera quadriceps are just big and beefy, over an inch long. They become interesting again when you learn that their colony doesn’t have a queen and every member can reproduce. How egalitarian. Instead of a queen, they have an alpha female, surrounded by up to five beta females, who do nothing all day but sit around waiting for the top spot to open. Sometimes a beta gets tired of waiting and decides to start laying eggs of her own. If the alpha female detects that her position is being challenged, she wipes chemicals from her stinger onto the would-be usurper. This triggers the workers to punish the offending ant. If I had to work all day everyday and you sit around waiting to inherit, I probably wouldn’t need much motivation. They pin the beta down and hold her there, sometimes for a few straight days. After the physical punishment is over, the beta is stripped of her rank, now just another lowly worker.
Specialized jobs are as common in ants as having six legs, but there was one that stopped me in my tracks and made me go back to the script to include them. Ever been on a road trip and been the one in charge of handing out the sandwiches? In my family, back in the station wagon days, which lasted at least a decade too long, that was the price you paid if you wanted to sit in the very back–anything to avoid being in the middle of the middle seat on top of the transmission hump. But the middle-middle seat looks pretty good if being in charge of the food means storing it inside your body. Introducing the honeypot ant, whose species you can find in both N.America and Australia. When food is plentiful, honeypot colonies select certain workers to be what entomologists call repletes and set them up in a safe spot. Then, the feeding begins. The other workers stuff them with food until the repletes’ abdomens swell up like balloons. They can be as big as a grape. I know a grape is hardly a benchmark for largeness, but when you’re an ant, that’s a helluva donk. When feast turns to famine, hungry workers go to the replete, give it a bit of a poke, and wait for calories to appear, courtesy of regurgitation. If the life of a replete doesn’t sound bad enough, sometimes rival ant colonies invade and kidnap them.
Honeypots aren’t just vending machines for their mates, they are a sweet treat for the indigenous people. To try some for yourself, first locate a honeypot hill, excavate it carefully and pick out some nice fat feeders, but just some of them. Be sure you leave some for the ants. And good news, you don’t have to prepare them, just pop ‘em in you gob like Gushers. Want something more savory? Try the Leafcutter Ant of South America. They’re eaten toasted and are said to have a “nutty, bacon-like taste,” at least according to companies that sell them pre-toasted. For something more refreshing, how about the lemon ants of the Amazon, whose taste comes from the formic acid the ants produce. Formic acid is named for formica, the Latin for ants, nothing to do with flooring. It’s supposed to be a chemical defense, but too bad for them, we like the taste.
If you’re ever in the Amazon, hacking your way through the dense rainforest, and suddenly the trees are less dense, and the incredible variety of plants, flowers and tree has turned into one kind of tree, the Duroia hirsuta, you know lemon ants are nearby, because you’ve found a devil’s garden. The hirsuta is the preferred habitat for lemon ants, Myrmelachista schumanni to give it its proper name. The locals believe these spots are the work of an evil spirit called the Chullachaki, while science had a few ideas of its own. One hypothesis is that D. hirsuta trees release toxic secretions that kill competing plants—a process botanists call allelopathy. Others argue that It’s actually the ants living on and in the tree that are responsible. The idea is that by killing other plants, the ants make room for new D. hirsuta saplings to grow, making more homes for their colony to expand into. The plants also benefit by increasing their biomass and eliminating the competition.
To test this hypothesis, researchers from Stanford located 10 devil’s gardens for the study and planted in the middle of them two Spanish cedar, one treated with a sticky insect barrier and the other left alone. They planted similar trees 150 yards away, still in the same forest, for more data points. They didn’t have to wait long for that data. Worker ants immediately attacked the untreated saplings by injecting formic acid into the leaves, costing the trees most of their leaves inside the week. The treated trees emerged unscathes. Well, they didn’t emerge, their trees, they just stand there. Unless there’s an Entmoot, then I don’t know. Anyway, researchers now had some pretty conclusive proof that it was the lemon ants actively killing anything that might compete with their tree buddies. The Stanford team noted, “To our knowledge this is the first record of an ant using formic acid as a herbicide—although it is known to have bactericidal and fungicidal properties.”
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If you’re still kicking around the jungles of Brazil, see if you can find any leaves that are precisely 25cm/10in off the ground. If you turn it over, there’s a chance you might find a carpenter ant with his jaws clamped to the leaf’s central vein. But he’s not there by choice and if fact, he’s long dead, another victim of Ophiocordyceps unilateralis, the zombie-ant fungus. If the scientific name gave you a little tickle of vague familiarity, perhaps you’ve played the video game “The Last of Us” or read or watched The Girl With All the Gifts. It’s those properties equivalent of the T-virus. When the spores of this fungus infect a carpenter ant, it takes about a week for it to grow all throughout the squishy ant body inside its exoskeleton armor. O. unilateralis drains that ant of nutrients and also, takes over its mind. It compels the ant to leave the safety-in-numbers of the colony and climb a nearby plant. It stops the ant at that oddly specific 25cm height, because that’s where the temperature and humidity are optimal for the fungus to grow. To make the ant doesn’t move, the fungus makes the ant lock its mandibles around a leaf. It’s not long after that that the ant dies and a long stalk begins to grow out of its head, a stipe topped with a capsule full of spores, ready to rain down more zombie-hood on the colony.
It’s also taken over the mind of one David Hughes, an entomologist at Pennsylvania State University, who has been studying O. unilateralis for years. To really find out what makes it tick, he had his student, by dint of a special microscope, slice infected ants wafer-thin, each slice 50 nanometers thick. To give you a frame of reference, a sheet of paper is about 100,000 nanometers thick. So ant slices that are 1/2000th the thickness of a piece of paper. Each slice was scanned, compiled into a three-dimensional model, and annotations were made on which bits were ant and which bits were fungus. It took three months to mark up just one muscle. No wonder he had a student do it. When the fungus first enters its host, it exists as single cells that float around the ant’s bloodstream, budding off new copies of themselves, like a bacterium myosing. At some point, these single cells start working together, connecting to each with short tubes, such as are also seen in fungi that infect plants. This allows them to communicate and exchange nutrients and communicate. Those tubes are unique; other fungi fatally infect ants, O. unilateralis is the only one that messes with their minds and Hughes believes those tubes are the key. They allow the fungus cells to be individuals but act in concert, just like the hive mind of the ants it infects. From there, they invade the ant’s muscles, either by penetrating the muscle cells or by squeezing between them and growing there. What’s perhaps most surprising from the mind-control fungus is that the ant’s brain is the only part of its body that *doesn’t have fungus in it. Hughes’s team found that fungal cells infiltrate the ant’s entire body, including its head, but they leave its brain untouched. Hughes thinks the fungus exerts direct control over the ant’s muscles, like tugging on the strings of a marionette. Once an infection takes hold, the ant’s motor neurons, the ones that carry messages from the brain to the muscles, begin to die and, it’s suspected, the fungus takes over, releasing chemicals that force the muscles to contract. So the poor little ant is probably still aware, but is just along for the ride.
Nobody said life as an ant would be pleasant. Just ask Cardiocondyla obscurior. Their colonies have a single dominant male, called the ergatoid, and he’s the very picture of territorial. If a new male comes a wooing, the reigning ergatoid will dab chemicals from his anus onto the intruder. This Dirty Anchez contains a kill scent, a pheromone that sets off the nearby workers, who swarm and kill the interloper. On the domestic defense side, the ergatoid goes through the nursery chambers, looking for day-old males to eliminate. He’s got to get them before their exoskeletons fully harden. They’re not just grappling, but trying to be the first to get that kill scent on the other. A two-day old has a 14% chance of winning and there’s a 43% chance they both die, Superman and Doomsday style.
Temnothorax pilagens, or pillage ants, are very small, and they raid colonies of ants that are themselves so small that the entire nest lies within a single acorn, like nature’s Polly Pocket, if polly had segments eyes and antennae and was several hundred individuals. These little acorn fortresses only have one entrance and the pillage ants walk right on in like they own the place. Nobody tries to fight them off. In fact, the acorn-dwellers don’t even notice them. Pillage ants use a chemical camouflage, like a Klingon bird of prey or the cloak of invisibility, depending on your fandom. It’s not 100% foolproof. If the pillage ant is found out and stealth mode turns to melee, they will stab their opponents in the neck with lethal paralyzing venom. The acorn ants rarely if ever score a kill, whereas the pillage ants can take out anywhere from 5 to 100% of the acorn ants. That’s extra impressive since pillage ants rarely send in more than four individuals at a time.
Mirror turtle ants probably wish they could do the no-smell-me thing. They follow hostile Crematogaster ampla ants to food and start trying to act like them. Mirror turtle ants don’t smell anything like C. ampla, so if they come within sniffing range, it’s game over. They have to move like the enemy and walk like the enemy, all while not getting too close to them, even though they’re in the midst of the enemy and stealing their food. Mirror turtle ants were the first species of ant documented to use visual mimicry to parasitize another ant species. And all so they don’t have to go through the effort of finding their own food.
You’ve got to keep your eye out for Solenopsis fugax as well. S. fugax steals the larvae of other ants, not to create a workforce, as a number of ant species do, but as food. They also tend to aphids to get the sweet liquid they excrete, called honeydew. So S. fugax are basically baby-eating ranchers. Baby-eating ranchers from a heist movie or the cold open of a James Bond. They tunnel into other nests, looking for the brood chamber, and when they find it, they discharge pheromones that repel the other ants for up to an hour. They gas the other ants and make off with the loot. And S. Fugax aren’t the only gas-attack ants. The African Crematogaster striatula specializes in hunting termites, the mortal enemy of the ant for millennia. They have a potent poison which induces death seizures in termites. Rather than waste time biting or stinging every single termite, they release it into the air as an aerosol spray to kill termites from a distance. Basically, C. striatula is nerve-gassing their way to victory. This is where I’d make a pun about the Geneva convention, but I couldn’t think of any. When C. striatula encounter a termite, they’ll raise their backside (gaster) in the air and point it at their prey. They must stretch before going into battle, because they can point their gaster in almost any direction. This aerosol poison also protects C. striatula against other species of ants. Researchers have never recorded any of these ants dying, because they were smart enough to turn around and run; the termites, not so much.
And that’s… In the first year of Biosphere 2, no one ant species was dominant. In 1993, populations of Paratrechina longicornis, aka crazy ants, which had not even been found in ‘91, had increased to extremely high levels. By 1996, virtually all the ants that could be observed (>99.9%) coming to bait were crazy ants. Crazy ants aren’t harmed by inbreeding, so a captive population isn’t harmed by a lack of new blood. If you’d like to hear more about the failure of Biosphere2, hmu on soc med. Remember… Thanks.. and please for me, for Mama LaBouche, for everyone’s sake, stay home this Thanksgiving. Just let this be a story you tell your future grandkids over nice, safe family dinners.