Ants
Like humans, ants have had an immensely complex and varied social evolution. It has culminated in the great ant societies with populations of a million or more individuals per colony. Frequently these colonies include specialized castes of workers and soldiers. They often support a variety of parasites and camp followers. Some herd other insects. Some enslave one another. ~ American entomologist Caryl Haskins
Ants evolved from vespoid wasps 110–130 MYA. Along with the rise of flowering plants, ants diversified, and gained ecological dominance 60 million years ago. In the process, finding strength in numbers, they left their wasp roots of solitary existence to live in gregarious eusocial colonies.
Ant success is spelled in multitudes. There are likely at least 1015 ants alive at any moment, with 22,000 extant ant species.
Ants have colonized almost every landmass on the planet, excluding only Antarctica and a few other remote or inhospitable locales, such as Greenland, Iceland, and the Hawaiian Islands.
Ants are superb ecosystem engineers. ~ English biologist David Edwards
The most abundant insects in the rainforest are ants, with quite different habitats. Some live on trees, in nests of leaves woven together. Others build subterranean caverns to nest in. A few find a home in rotten wood.
Army ants nest nowhere. They are relentlessly on the move, briefly resting in bivouacs.
South American leafcutter ants may destroy more foliage than all other creatures put together. Other ants have more benign, even beneficial, relations with plants.
Some seeds are structured to allure ants into carrying them away. While many such seeds are eaten, some survive to sprout far from where they were picked up, thus aiding floral distribution.
The rainforest is an ant mosaic. Almost all other animals are influenced by ants. Some are harbored and protected. Many more are attacked and eaten.
Ant success comes from adaptability: the ability to solve complex problems via swarm intelligence, coevolution with other species, and a highly developed social organization.
Though social complexity varies considerably, ants are uniformly eusocial insects. Isolated ants die of loneliness.
Ant colonies consistently differ in coping style—some are more risk-prone, whereas others are more risk-averse. ~ American behavioral biologist Sarah Bengston & German biologist Anne Dornhaus
Castes
Several ant species have colonies with multiple phenotypic castes. By creating specialists, a caste system optimizes social organization. Individuals are caste-bound via histone modifications, an epigenetic mechanism.
Even ant species that don’t physically specialize have functional roles. 3 castes are common: nurses, cleaners, and foragers.
Ants in different castes cluster together, rarely interacting with ants in other groups. Nurses that tend to the queen and brood spend their time deep within the nest, while foragers hang out near the nest entrance.
Cleaners are an exception. Roaming throughout the nest as part of their duties, cleaners interact with other cliques.
Ants commonly change careers as they get older. Typically, nurses graduate to nest cleaning. Cleaners transition to foraging as they age.
Career by age is not clear-cut. There are young foragers and old nurses. As with bees, aptitude and inclination play a role in the role that an ant plays within her colony. Every ant has her own personality.
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Ground-dwelling ants have a massive genomic database dedicated to sensory reception that matters most: 400 genes for odor, and 116 for taste. A honeybee has 179 genes for odor and 76 for taste.
Harvester ants are exemplary in efficient foraging. They avoid congestion and maximize gathering by allocating resources based upon feedback loops.
A harvester ant is slow to return to the nest unless it finds something. The faster foragers return, the more ants are sent for seeds in the same direction.
If returns become tardy, or without produce, the supply line is thinned, or the search called off. Ants leave pheromone trails that allow timing studies for foraging efforts. In sum, ants are efficiency experts.
A critical aspect of efficiency is resource allocation. A sizable minority of ants at any one time aren’t up to much, while a small minority do most of what is being done.
30% of the fire ants digging a tunnel may do 70% of the work. There may be many ants nearby (but out of the way), slacking off. The reason: avoiding getting in each other’s way.
Ants know that traffic jams greatly impede efficiency. If an active worker wants a break, she is instantly replaced. A surplus labor force as practiced by ants is the most productive and the most accommodating to worker wants and needs. Some ants are industrious, others not so much.
Collectively carrying a large load requires a high degree of coordination. One facet of this coordination is the requirement to align forces such that inefficient tug-of-wars are avoided.
~ Israeli myrmecologist Ofer Feinerman et al
Ants can carry large, heavy objects to their nest because they intelligently coordinate.
While the combined force of the group determines the speed of the load, individual informed ants steer the direction of movement. ~ Ofer Feinerman et al
Queens
An ant colony, like a beehive, is full of sisters, with a sprinkling of drone males, useful for their meager reproductive contribution and little else. Unlike honeybees, which have a single queen, ant species commonly have colonies with multiple queens.
Supercolonies
The Argentine ant is native to southern South America. Discovered on its home turf, the Argentine ant was termed humble (Linepithema humile). That sentiment was not to last.
Both Argentine and fire ants are wildly prolific invasive species, spread abroad by hitching rides on human transport. Fire ants comprise 285 species of stinging ants worldwide.
Both ants have 2 distinct colony types. The difference involves genetic expression, which results in behavioral differences.
In their native lands, these ants have single-queen colonies, with a few hundred thousand workers. Such colonies are territorial. This keeps their numbers in check.
The invasive attainment of these ants owes largely to numerical superiority. In their new lands, these ants form supercolonies with multiple queens. A supercolony may have billions of members, stretching an expanse of 6,000 km or more.
The rivalry between native and invasive ants is not won by conflict. Instead, adoption of supercolonies enables these ants to have superior foraging success, often at the expense of competitors.
Supercolonies are actually a networked system of nests, each hosted by single queens, sufficiently related that workers from neighboring nests go about their business when they meet rather than getting into a spat.
As there is no aggression between adjacent colonies, no energy is expended in rivalry that would otherwise prove costly. Cooperation enables economies of scale, and superior success as invasive species.
Colonies Without Queens
~100 ant species form colonies without queens. Female workers mate and reproduce. But almost all don’t, because queenless ants run a rigid social dominance hierarchy.
Females fight fiercely for the right to mate. Only 1 wins top spot, and thereby entitlement to breed.
The fighting does not stop there. Battle bouts continue for 1st runner-up, 2nd, and so on down the line.
The winner physiologically changes. Her ovaries become active. She exudes a fertility pheromone that tells her social status. And, after insemination, she starts laying eggs.
Her reproductive success lasts only as long as her scent. If her fertility pheromone level drops, the runner-up aggressively acts to replace her.
An analogous system exists in several mammal species, but with males fighting for mating rights with females.
Dinosaur Ants
The more primitive the ant, the less socially integrated and organized; and so, a smaller colony. (The common term primitive is used as a shorthand for early evolved.) The dinosaur ant is so named because it is a primordial ant. This Australia native is the only still-living species of its genus.
Dinosaur ant colonies are small, with only ~50 members. While they will defend their nest to the death if invaded, they cannot afford to maintain a foraging territory. Such aggressive behavior runs the risk of loss of life; a cost too high to countenance. A colony so small cannot afford the empire building of more complex societies.
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By contrast, weaver ants are among the most socially sophisticated ant, with colonies 10,000 times that of dinosaur ants. Yet put a dinosaur ant worker next to a weaver and you can hardly tell them apart.
The difference is in the behavior. Disturb a dinosaur and she freezes or flees. No sister comes to her aid. Faced with the prospect of a fight, a dinosaur demurs.
Upset a weaver ant and prepare to die. She will attack. She will call and get help. Within 5 to 10 seconds, a swarm of weaver sisters will descend with unmatched fighting spirit. Hell has no fury like a weaver ant scorned.
For their size, ants are among the strongest animals. The average worker ant can lift 20 times its own body weight.
Ants don’t have ears. They hear by feeling ground vibrations through their feet.
Ants don’t have lungs. They breathe air by holes (tracheae) in their abdomens, exchanging oxygen in and carbon dioxide out the same openings. Ant breathing rate is comparable to a human during moderate exercise.
Communication
Ants have complex communication systems. Like all insects, chemical communication is a norm. Ants employ about 20 different pheromones, though they also use body language and tactile information exchange, not unlike humans.
Ants are altruistic to their own. An ant asked by a sister for food gives some of what she has. Unfortunately, such generosity may be taken advantage of, though not by a sister.
Wheedled by Beetles
Some other insects understand ant language. Ants may be beguiled by beetles.
The European turtle beetle approaches a food-laden shining black ant and asks for something to eat by imitating an ant: touching the ant on the lip to induce regurgitation. The ant obliges.
If the ant realizes she has been tricked, she attacks. The beetle withdraws into its shell, turtle-like.
Other beetles imitate ant scent, allowing them to live unmolested inside an ant colony, tricking the ants into feeding them, and even nursing the beetle larvae which feed on the ants’ brood.
For ants, chemical communication is trump. Those that can secrete the lingo have ants at their mercy.
Rove beetles, while less communicative, are more dangerous. One of a pack of roves immobilizes an ant by biting the back of her neck. The beetles then drag the ant away: abducted for dinner.
If the roves are caught out, they have a perfected defense. The beetles secrete an appeasing scent from glands at the tip of their abdomen, ameliorating the aggression and allowing their escape.
Ant Sounds
It was long presumed that ants were almost exclusively chemical communicators, but sound is significant to some ant genera, such as Myrmica, with over 200 diverse species that live throughout Europe and Asia.
Myrmica have a specialized spike along their abdomen which they sometimes stroke with their hind legs, making a sound similar to dragging the teeth of a comb along the edge of a table. This is used as an emergency beacon: a way to shout for help when threatened by a predator.
Larvae and young pupae have soft outer skeletons, and so are soundless. As pupae mature, their exoskeleton hardens. Older pupae have fully functional spikes. They use these spikes to signal caretakers their need for attention.
The sounds they make rescue them by signaling their social status. There is complex information in these signals. ~ English entomologist Karsten Schönrogge
Acoustic communication is especially important at the late pupal stage, because mature pupae have yet to produce the full array of adult pheromones, but they do not smell nor behave like larvae.
There is another benefit to the sound of the spike. This ant genus is subject to several inquiline species: certain Myrmica species that prey upon others in the same genus, by using their host for brood parasitism and other advantages. The larvae of the butterfly genus Maculinea also live in Myrmica nests, either directly feeding upon the ants or being fed by them.
A parasite ant species is unable to sustain its own colony. Instead, it contributes to the host colony at certain stages of its life, while relying upon host resources at other times.
Inquiline is a somewhat slippery term. Parasites are by definition deleterious to their hosts. In contrast, inquilines gain from their host association, by taking advantage of host services and facilities, but do not necessarily bring their hosts down.
The specialized spike that Myrmica have allows the mature pupae to signal their need, and thus supersede any inquiline competitors for caretaker attention. Thus, the potential damage of brood parasitism is mitigated.
Leafcutter Ants
Ant colonies are more than the sum of their parts. They are operational units with emergent traits that arise from complex interactions of colony members. The ultimate possibilities of superorganismic evolution are perhaps best expressed by the spectacular leafcutter ants. ~ Bert Hölldobler & Edward O. Wilson
Leafcutter ants belong to the attine group of leaf consumers, with 2 genera and 47 species. Attine ants are most abundant in the tropical forests of Central and South America.
Winged attine ants, male and female, fly from a nest en masse in a nuptial flight. They mate in the air, mostly at night.
Males are hatched from unfertilized eggs and contribute nothing except sperm. They are genetically programmed to expire shortly after their nuptial flight.
Each female mates with multiple males, storing the 300 million sperm needed to start a new colony. Leafcutter ants are among the most fertile animals known.
Once sufficiently impregnated, a queen loses her wings and scrounges for a suitable spot to nest. She digs a narrow tunnel, down 20–30 cm, then creates a single 6-centimeter chamber.
Before her mating flight, a queen packs a small wad of symbiotic fungus into her infrabuccal pocket, which is located at the bottom of her mouth. This mycelium is fed with her first eggs. If the initial fungus culture dies, the incipient colony is doomed.
A few emergent queens lose their wings before their nuptial flight. Unfertilized, their chance to establish a new colony is finished; so they change roles: staying with their mother colony to help in its defense.
Only about 2.5% of the queens have the good fortune to found a long-lived colony. A colony of leafcutter ants is like no other.
From a single tiny hole, a colony expands into a labyrinth of chambers. Many chambers near the surface have fungus gardens.
Fully developed, a single leafcutter nest may house a thousand gardens, in a subterranean antropolis up to 30 meters across and 5.5 meters deep, taking up anywhere from 30–600 square meters, with up to 10 million colonists.
36 tonnes of soil may be excavated in digging a leafcutter nest. Cavernous perimeter tunnels, which may extend 8 meters from the nest, make a beltway around that defines the subterranean city.
A leafcutter colony may last for a decade or more. The depth of a nest is limited only by the water table below.
As a colony matures, leafcutters are organized by caste. All are daughters of the queen, who may lay 50 million eggs in her lifetime. The young females, kept infertile by hormones from mother, become workers.
Leafcutters are morphologically caste-bound. Each caste performs a different basic function.
A worker’s caste is determined by how much fungus they were fed as larvae. The different castes are based mostly on size.
Attine ants are highly polymorphic. There is a 7 times difference in body size between the largest and smallest caste members, and hundreds of times difference in weight.
Up to 7 physical castes are present in mature colonies, including the queen, which outsizes all others. 4 worker castes are notable: majors, medias, minors, and minims.
Majors are large soldiers, acting in defense of the nest, trail clearance, and hauling bulky items back to the nest. Soldiers check out other ants in their path with their sensitive antennae. Encountering an enemy results in releasing a chemical alarm (pheromones) that summons others. The pheromones drive soldiers into a killing frenzy.
Medias forage, cutting leaves and bringing the fragments back. If a leafcutter encounters a soft fruit, it eagerly engages in cutting chunks for carriage to the nest.
Leaf-cutting technique is like an electric carving knife. A media stridulates: rapidly oscillating her hind end, vibrating the mandible as a cutting tool. The sound attracts other workers to the site.
The craft of a media worker is circumscribed by biology. A media starts her career as a leafcutter with scalpel-sharp mandibles, but repetitive slicing dulls the V-shaped blades in time. A dull mandible means that it takes twice the energy and time to cut a leaf, compared to a young blade.
Rather than retire as a forager, older medias change their career to carrying sheared-off vegetation back to the nest. Cut leaf fragments may be several times larger than the ant carrying it.
Each worker runs an estimated human equivalent of a 4-minute mile for up to 50 km, lugging 225 kg. For efficiency, foragers follow one another, forming a distinct line, and thereby carving noticeable paths through the forest.
To maintain rapid transit, trunk routes are kept clear of vegetation by road workers. These roadways are static and long-lived; an extension of the nest architecture.
Leafcutters are smart workers. When foragers sense rain coming, they hustle back to the nest with what they have got. A wet leaf fragment weighs more than double a dry one: too much to make the effort worthwhile.
Leafcutters in a caste take specialized jobs according to ability and immediate need. With hundreds of thousands to millions of workers carrying out a variety of coordinated tasks, the foraging effort is an extremely well-choreographed production. Pheromone markings and other signals create an information network which facilitates discovering and exploiting the highest-quality resources available.
Heads Up
Workers are subject to pests, notably the parasitoid phorid fly, of which there are 110 known species. A phorid will try to land on an ant’s thorax and plant eggs.
Larvae hatch and head to the head, where they devour the ant’s brain, during which the ant wanders aimlessly for a couple of weeks. After that, the head falls off by enzymatic decapitation. The larva releases an enzyme that dissolves the membrane keeping the ant’s head attached to its body. The fly pupates in the head capsule for a couple of weeks, before emerging as the next generation of threat.
To thwart the prospect of losing one’s head, medias keep lookouts when hauling leaves. The small ants ride shotgun on leaves to keep the flies at bay when the hauler cannot defend herself.
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Majors are 3 times larger than minors but are overwhelmed numerically. Minors are the first line of defense, continuously patrolling the terrain, especially the foraging lines.
Fungus Farming
Tiny minims are fungiculturists: tending gardens of domesticated fungi. While leafcutter species each cultivate their own species of fungus, all leafcutters like the Lepiotaceae fungus family.
Leafcutters and Lepiotaceae are thoroughly mutualistic. Their bond is such that neither is found in Nature without the other.
Though some leaf sap is consumed, harvested leaves themselves are indigestible to the ants. The cuttings serve as fodder for the Lepiotaceae. Leafcutters cultivate bacteria which render the leaves digestible to fungi.
There is an ancient symbiosis between ants and fungus. 200 known ant species cultivate fungus. Most ants feed their fungus dead organic matter: plant debris, caterpillar feces, insect corpses. Only leafcutters deliver fresh produce. Leafcutter fungiculture is a culmination of fungus farming that is not unique to ants. Ambrosia beetles and termites also practice fungus-based agriculture.
Leafcutters took to feeding fungi fresh leaves ~10 MYA. Ants growing fungus on dead and decaying leaves predate leafcutters by ~50 million years.
Since the leaves are largely fungus food, the ants need to be careful that their gardens don’t overdose on the chemical defenses that any particular plant may have. The minims chemically listen to Lepiotaceae, which tells them which leaves it likes. If a certain leaf is toxic, minims tell medias to stop bringing that plant.
The fungus is fed to ant larvae. Adults live largely off leaf sap, topped off by fungus and yeast. The larvae need the fungus as food, while the fungus needs ant-tending to thrive.
By replanting hyphae on their carpet of vegetation, ants prevent fungal spore formation and sexual reproduction. To the ants, spores are superfluous, as they do not eat them.
Because of this practice, the fungus relies upon the ants to achieve asexual reproduction, just as the ants cannot get enough to eat without their fungus gardens.
Like other fungus-growing ants, leafcutters fertilize the colony’s fungal gardens with their own manure. The fungal enzymes that break down plant matter are preserved despite ant digestion.
From this, Lepiotaceae can recognize whether the ants have eaten from a different fungal source. This information carries throughout a colony’s fungus gardens, and the fungus reacts negatively.
Introducing an alien fungus lowers garden productivity, which in turn affects the ant colony. Hence, the ants’ manuring practice regulates the symbiotic relationship, obliging a colony of leafcutters to a single fungal strain. A neighboring leafcutter colony may cultivate a different strain.
Killer Mold
Minims cultivate the fungal farm, feeding it with freshly cut leaves, grooming it, cleaning it, pruning it, and keeping it free from pests, especially the parasitic mold Escovopsis weberi.
This mold does not compete with the cultivar by eating living leaf fodder. Instead, E. weberi is necrotrophic: living off dead organic matter. It kills the cultivar before it consumes Lepiotaceae, the leafcutter’s fungal crop.
Molds often invasively infect, then kill their host. E. weberi instead slaughters Lepiotaceae by secreting compounds that break down the cultivar’s cellular structure. E. weberi has a history of leafcutter coevolution parasitism going back at least 50 million years.
Leafcutters have another symbiotic partner to counter mold: Streptomyces bacteria, which grow in a specialized area of the ant: the metapleural glands. The bacteria secrete an antifungal compound onto the surface of the ant’s exoskeleton to kill the mold that would otherwise foil a fungal farm.
A leafcutter’s Streptomyces is one of over 500 species of this bacteria, which, as a genus, have a wider habitat: soil and decaying vegetation. Various Streptomyces provide 2/3rds of the naturally derived antibiotics that humans use.
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Nitrogen-fixing bacteria are yet another symbiont in leafcutter colonies. Leafcutters maintain a clean vegetative substrate that engenders bacterial nitrogen-fixers. The bacteria convert atmospheric nitrogen to ammonia, a bacterial waste product that serves as a basic building block of amino acids and proteins for the ants.
Hygiene
Leafcutters are hygienic. They keep their gardens immaculate through a variety of practices: plucking out alien fungi and other waste, inoculating the correct fungal mycelia onto fresh substrate, fecal fertilization, antibiotic secretion, and application of growth hormones.
Temperature and humidity inside the colony are tightly regulated. Leafcutter nest architecture is constantly managed to adjust for ambient conditions outside the colony.
Especially owing to the constant threat of parasitic mold, waste management is crucial to colony longevity. Larger, deeper pits than fungal gardens, at the bottom of the nest, hold waste.
Garbage is deposited at designated waste stations, then transported to central waste pits. The pits are like a trash chute. They are located directly below openings to the surface, allowing proper ventilation. Soil covers notably noxious pits.
The risk of infection is higher in waste workers than in other occupations. Waste transport and disposal duties are taken by older, more dispensable ants, who only have a few weeks life left at most. Older workers taking jobs with greater risks, in a variety of contexts, is common to many ant species.
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Leafcutters are the chief herbivore of the New World tropics: harvesting ~15% of the leaves produced in a rain forest. Yet leafcutters are savvy enough to not kill trees: they shift between plants.
Foragers prefer to harvest leaves from drought-stressed flora. On any plant, vigorously thriving leaves are bypassed in favor of stressed leaves, which contain higher concentrations of valued nutrients. This minimizes the toll on plants.
Leafcutters have a larger perspective on their foraging. Their harvesting depends not only on certain leaf traits, but also accounts for the ecosystem as a whole. Leafcutters live a sustainable existence.
Overall, leafcutters play a positive ecological role, aerating areas of soil in grasslands and forests. Native palms sprout from the mounds of expiring colonies.
The sophistication of cooperation, nest architecture, and maintenance, and their assembly-line farming, render leafcutter ants an impressive apex in the animal kingdom. Only modern human colonies approach leafcutters in complexity. By comparison, people are ecologically insensitive dullards, lazy, and badly disorganized.
Another ant has carved a similar lifestyle, albeit adapted to an arboreal habitat.
Weaver Ants
Whereas leafcutter ants cut leaves as fungus fodder, weaver ants build their nests from leaves. Weaver ants live in the tropical forests of Africa and India, as well as Australia and the Solomon Islands.
Highly organized, separate teams of workers bend leaves and glue them together to form nests, “in size between that of a man’s head and his fist,” scribed English naturalist Joseph Banks in 1770.
The glue used to hold the leaves comes from mature larvae. While a leaf is held together by a leaf-tugging team, each of a coordinated sewing team holds a larva between its mandibles, swinging a larva back and forth, spinning connections between leaves; signaling with their antennae to the larvae to release sticky threads from glands below the larva’s mouth. The larvae donate all their silk to the communal cocoon.
The size of leaf-weaving teams varies by need. After a few ants have managed to bend a leaf onto itself or toward another leaf, nearby workers join in.
If the span between leaves is beyond the reach of a single row of ants, workers form chains: an extension ant grasps the ant in front by the petiole (waist). Numerous intricate chains may be formed in unison to bring together large leaves.
As with other social ants, weavers communicate with pheromones and tactile signals; but weavers know their roles and act according to what is going on.
A leaf nest can be built within 24 hours and may last more than a month. A nest is strong and watertight. Meanwhile, ants continually build new nests: replacing deteriorated ones and those damaged by storms.
Nest-building is strenuous activity. Weavers are up to it. They can hold onto something more than 100 times their own weight while hanging upside down without losing their grip on the branch they are hanging from.
Weaver ant tarsi have moist, expandable food pads that can adhere to surfaces via capillary forces. Ants control these pads to move, or stay stuck, as need be. Reaction time is a millisecond. The fastest known nerve reflex response takes 5 milliseconds, so the ants’ quick grip must be mechanical, controlled energetically.
A single colony may have half a million weavers, scattered among 150 nests in as many as 20 trees. A weaver colony may patrol 1,600 square meters, one of the largest territories known for insects. Weavers are the dominant ant in their domain.
Among their own species, weavers generally respect each other’s territories, though neighboring colonies may occasionally battle for territory. Colony boundaries are clearly marked, with a no-ant’s-land strip between border lines.
Weaver ants recognize neighbors by scent. Once an ant has had an encounter with a rival, it goes back to the colony and passes this information on: how the rival smelled, and how aggressive the interaction was.
This intelligence is shared among workers. Contacts with rivals is continually updated among nest mates. Ants adjust the aggressiveness of their responses based upon the colony’s experiences.
Inside the silk-walled nests are dairies. Weaver ants tend sap-sucking scale insects, collecting honeydew (a sugary sap) secreted from the bright red scales of adults. The scales thrive under the care of the weavers, producing gold-colored young.
As with many other ant species, weavers are morphologically specialized, with different worker castes. The smallest weavers – minors – lick the scales to clean them and collect the discharge: a honeydew which they regurgitate upon demand, whereupon a receiving larger sister transports and distributes the produce to others in the nest.
Larger workers – majors – have various duties depending upon age. Young majors tend the queen, larvae, and pupae. Middle-aged majors forage.
Senior majors, some missing a leg, or with worn mandibles, protect the colony as scouts and guards. They retain sharp eyesight and acute sense of smell and have the added advantage of life experience. Seniors are also the most expendable.
The dairies are a supplement to the weavers’ diet. Weavers primarily eat other insects, including scorpions, but are not beyond more exotic fare, such as snake, crab, or bird. Workers share their harvest – partly digested and regurgitated – with the brood.
A worker spots a banquet: more than it can handle alone. The worker releases a short-range recruiting pheromone to call nearby colleagues, who race to assist. They spray the prey with formic acid (a common venom in ant bites and bee stings), grab the prey and hold it, limbs splayed, until it is subdued.
Weaver ants hunt practically any invertebrate big enough to be a meal. They are such effective hunters that weaver ant territories typically have lower populations of other insects than those areas outside weavers’ hunting grounds.
The insects that weavers eat are often plant pests, so weavers benefit plants by decreasing herbivory. Weaver colonies have been employed in citrus orchards for pest control in China and Southeast Asia since at least the 5th century.
Fruit trees with weaver ants produce higher-quality fruit and suffer less leaf damage from herbivores. The blessing is mixed, as weavers are a frightening foe, and so limit pollination by insects, and fruit removal by birds and mammals, thereby reducing seed dispersal. The scale insects and leafhoppers that weavers farm for honeydew also take their toll on trees.
There are weaver ant predators. Some caterpillars lure ants with their sweet honeydew scent, giving them entry to a nest, where they devour ant larvae.
There are species of jumping spiders that resemble and smell like weaver ants. This deception affords entry into a nest without provoking an attack. Once inside, a spider feasts on eggs, larvae, and ants.
Weaver ants also preyed upon by humans. In Thailand and the Philippines, weaver ant pupae, which have a creamy flavor, are harvested and sold in food markets. Adult ants, with a lemony/creamy/sour taste, are also delectable.
Meat Ants
The meat ants of Australia are also known as gravel ants, because they often place sand, pebbles, mollusk shells, and/or vegetation scraps (leaves, twigs) on their nest mound near the opening, which help heat the nest quicker in the morning. Home decoration is not the meat ant’s only domestic skill.
Like other ants in their genus, meat ants enjoy symbiotic relationships with certain caterpillars and butterflies, as well as leafhoppers and the like. The caterpillars and leafhoppers secrete honeydew and are rewarded with protection from predators. This comprises the greater portion of a gravel ant’s diet, which is supplemented with heartier fare.
Besides the sweets, meat ants are omnivorous scavengers. Their name comes from their employment by farmers to clean carcasses. Meat ants also scavenge for dead but still juicy invertebrates.
Meat ants reside in underground nests with up to 64,000 members. Satellite colonies are often formed by daughter queens near the nest, resulting in connected nests that form a supercolony, stretching up to 650 meters.
Nest holes are regularly arranged. Each nest has its own branched network of tunnels, with a few connections to other nests in the supercolony.
Meat ants are diurnal. On hot days, the ants take a siesta midday, owing to the intense heat. All activity stops.
Unlike many ant species, meat ants do not have physical castes of workers and soldiers. But they do take different roles. Tasks are designated by ability and experience level, as well as age.
Young ants act as caretakers for eggs and larvae in the nest. The next step, for more mature ants, is to food collection from stationary resources: honeydew harvesting from true bugs or caterpillars and dragging dead animals back to the nest for communal feasting. This is often a group effort. Older ants forage solo, collecting small invertebrates and building materials.
The oldest, toughest ants compete with ants from other colonies for territorial rights. Meat ants engage in non-lethal ritual combat with ants from neighboring colonies to establish foraging boundaries. Chemical communication is used to make a point and settle a score.
Meat ants are also aggressively competitive with other ant species, tending to dominate their local ant communities. Other ant species either exploit resources not favored by meat ants, forage at different times, or live elsewhere.
Cane Toads
Venomous cane toads, native to Central and South America, were purposely introduced into Australia for agricultural pest control: to eat cane beetles, which damage sugar cane crops. What was not anticipated, or even considered, was that cane toads successfully compete with native species, disrupting the local ecosystem. This should have been foreseen considering a cane toad’s special talent.
The cane toad has poison glands behind the ears that take them off the menu of would-be predators or take out the would-be predator who tries to eat them, which leads to local extinctions from toad-kill. Even the tadpoles are highly toxic. But not to meat ants.
A cane toad’s defensive strategy is to sit still and let its poison do the talking. For a meat ant, that turns the toad into a statuesque banquet. Meat ants will mass to eat a toad alive, taking hunks to the nest; spicy fare for the family back home.
