Ant

• 1. Introduction

  ›

  Ants are among the most successful animals on Earth. Right now, somewhere between one and ten quadrillion of them are alive at this moment, according to an estimate by myrmecologist E. O. Wilson from 2009. More careful calculations published in 2022 put the figure at around 20 quadrillion and place the total dry carbon mass of all ants at 12 megatons, exceeding the combined biomass of every wild bird and mammal on the planet.

  They live on every continent except Antarctica. They have been here since the Cretaceous period, more than 100 million years ago, evolving from ancestors related to stinging wasps. Today more than 13,800 species have been formally described, from the 0.75 mm specks that are the smallest workers to the fossil Titanomyrma giganteum, whose queen reached 6 cm in length with a wingspan of 15 cm.

  What makes ants so enduring? How do creatures without lungs, without closed blood vessels, and with brains small enough to fit on a pinhead manage to build bridges, wage wars, farm fungi, and teach each other? This is the story of a family called Formicidae, and the questions their existence forces us to ask about intelligence, society, and what it means to cooperate.

• 2. Ancient Origins

  ›

  In 1966, E. O. Wilson and his colleagues identified fossil remains of an ant called Sphecomyrma, trapped in amber dating to around 92 million years ago. The specimen carried features found in some wasps but not in modern ants, making it a critical bridge between two insect lineages. It was physical proof of what the evolutionary record had long suggested: that ants descended from within the stinging wasps.

  The oldest ant fossils known date to the mid-Cretaceous, roughly 113-100 million years ago. These belonged to extinct stem-groups including the Haidomyrmecinae, Sphecomyrminae, and Zigrasimeciinae. Modern ant subfamilies began appearing toward the end of the Cretaceous, around 80-70 million years ago. During the Cretaceous, a few primitive species ranged widely across Laurasia, the ancient Northern Hemisphere supercontinent, though their remains make up only about 1% of insect fossils from that era.

  The real explosion came later. Ants diversified extensively during what researchers call the Angiosperm Terrestrial Revolution and assumed ecological dominance around 60 million years ago, at the start of the Paleogene period. By the Oligocene and Miocene epochs, ants had come to represent 20-40% of all insects found in major fossil deposits. A 2021 study by Fernandez et al. suggested the common ancestors of ants and their closest relatives probably existed as early as the end of the Jurassic period, before diverging in the Cretaceous. The fossil amber of the Dominican Republic, apparently from the early Miocene, contains genera of which 92% survive today.

• 3. Architecture of a Body

  ›

  An ant's exoskeleton does the work that bones do in a vertebrate body: it provides a rigid casing and anchor points for muscles. Oxygen moves in and out not through lungs but through tiny valves in the exoskeleton called spiracles. There are no closed blood vessels; instead, a thin perforated tube called the dorsal aorta runs along the top of the body and pumps haemolymph toward the head.

  The body divides into three sections: the head, mesosoma, and metasoma. A distinctive node-like structure called the petiole forms the narrow waist between the midsection and the abdomen. This petiole, along with elbowed antennae and metapleural glands, immediately distinguishes ants from all other insects.

  The head alone contains multiple sensory systems. Compound eyes built from many tiny lenses detect movement with precision but produce a blurry image overall. Three smaller ocelli on top of the head read light levels and polarization, helping ants navigate by the position of the sun. Australia's bulldog ant stands out here, capable of discriminating the distance and size of objects moving nearly a meter away. Experiments have also shown that species including Camponotus blandus, Solenopsis invicta, and Formica cunicularia possess a degree of color vision.

  The mandibles serve as the ant's primary tool. They carry food, construct nests, manipulate objects, and deliver defence. In some species, a small internal pocket called the infrabuccal chamber stores food inside the mouth, ready to be passed to nestmates or larvae by trophallaxis, a process of regurgitation that also functions as a channel for chemical information within the colony.

• 4. The Colony as Organism

  ›

  A typical ant colony consists of castes of sterile, wingless females. Most are workers called ergates; a specialized subset, dinergates, serve as soldiers with larger heads and correspondingly stronger mandibles. Nearly all colonies also maintain fertile males called drones and one or more fertile females called queens, known formally as gynes. Colonies are described as superorganisms because the ants appear to operate as a unified entity.

  The life cycle begins with an egg. Fertilized eggs become diploid females; unfertilized ones become haploid males. Larvae are fed by workers through trophallaxis and pass through four or five molts before entering the pupal stage. The first workers to hatch from a new colony, called nanitics, are smaller and weaker than later workers but begin serving the colony immediately. A new worker spends her first days caring for the queen and young, then moves to nest construction, and finally to defence and foraging as she ages.

  Queen ants can live for up to 30 years. Workers survive from one to three years. Males are more transitory, living only a few weeks. Ant queens are estimated to live 100 times as long as solitary insects of a similar size. In honeypot ants such as Myrmecocystus mexicanus, young workers are fed until their abdomens are distended and they serve as living food storage vessels called repletes. If repletes are removed, other workers take on the role, demonstrating a flexibility that runs throughout ant social structure.

  Colony membership is maintained chemically. A signature blend of surface chemicals called cuticular hydrocarbons forms a colony odor that every member can recognize. Any ant entering a colony without the matching scent is attacked. In the Argentine ant Linepithema humile, this recognition extends across remarkable distances: workers from colonies anywhere in the southern United States and Mexico are accepted by colonies throughout the same region, while those same ants are not accepted by Argentine ant colonies established in Europe.

• 5. Communication and Learning

  ›

  Pheromones, sounds, and touch form the communication network of an ant colony. Foragers mark trails on the ground with scent chemicals; other ants follow those trails and reinforce them on the return trip. When a food source runs out, no new trails are laid and the scent fades. When a path is blocked, foragers explore alternatives and the shortest successful new route becomes the dominant trail as more ants reinforce it.

  A crushed ant emits an alarm pheromone that drives nearby ants into an attack frenzy and draws more ants from farther away. Some species deploy what researchers call propaganda pheromones to confuse enemy ants and cause them to fight each other. Pheromones are produced by structures including Dufour's glands, poison glands, and glands on the hindgut, pygidium, rectum, sternum, and hind tibia. They are also passed through trophallaxis, allowing ants to detect which task group a nestmate belongs to.

  Beyond chemical signaling, some ant species produce sounds through stridulation using segments of the abdomen and the mandibles. Ants may also be the only group outside mammals where interactive teaching has been directly observed. A knowledgeable forager of Temnothorax albipennis leads a naive nestmate to food through a process called tandem running. The leader actively adjusts its pace in response to the follower's progress, slowing when the follower lags and accelerating when the follower gets too close.

  Controlled experiments with colonies of Cerapachys biroi showed that an individual may choose nest roles based on prior experience. When one group of identical workers was repeatedly rewarded in foraging and another group consistently failed, the successful group intensified its foraging while the unsuccessful group shifted over the following month to specializing in brood care.

• 6. Defence and Weaponry

  ›

  Bullet ants of the genus Paraponera, found in Central and South America, deliver the most painful sting of any insect by the measure of the Schmidt sting pain index. The sting of jack jumper ants can be lethal to humans; an antivenom has been developed specifically for it. Fire ants of the genus Solenopsis are unique among ants in carrying venom containing piperidine alkaloids, painful and potentially dangerous to people with hypersensitivity.

  Trap-jaw ants of the genus Odontomachus take a different approach. Their mandibles snap shut faster than any other predatory appendages in the animal kingdom. A study of Odontomachus bauri recorded peak jaw speeds between 126 and 230 km/h, with closure happening within 130 microseconds on average. The ants also use their jaws as a catapult, ejecting intruders or flinging themselves backward to escape. Energy is stored in a thick band of muscle and released explosively when sensory organs resembling hairs on the inside of the mandibles are stimulated.

  A Malaysian species in the Camponotus cylindricus group carries an extreme form of colonial self-defence. Its workers have enlarged mandibular glands extending into the abdomen. If combat turns against them, a worker ruptures its own abdominal membrane, releasing a poisonous secretion containing acetophenones and other chemicals that immobilizes small insect attackers. The worker dies in the act.

  Colonies also guard against pathogens. Secretions from the metapleural gland, unique to ants, produce chemicals with antibiotic properties. In Megaponera analis, injured workers are treated by nestmates with these secretions. Camponotus ants, which lack the metapleural gland, have developed a different response: workers of Camponotus maculatus and C. floridanus amputate the injured legs of nestmates when the femur is damaged, as a femur injury carries a greater infection risk than a tibia injury.

• 7. Relationships Across Species

  ›

  Aphids secrete a sugar-rich liquid called honeydew as they feed on plant sap. Many ant species collect this honeydew and in return keep predators away from the aphids, moving them between feeding sites and even carrying them to new areas when the colony relocates. Mealybugs receive the same protection; mealybugs can become a serious pest of pineapples when ants are present to shield them from their natural enemies.

  Leafcutter ants of the genera Atta and Acromyrmex feed exclusively on a fungus that grows only within their colonies. Workers continually bring back cut leaves, which are processed in fungal gardens by workers sized for each task: the largest ants cut stalks, smaller workers chew the leaves, and the smallest tend the fungus. The ants are sensitive to chemical signals from the fungus; if a leaf type proves toxic to it, the colony stops collecting that plant entirely.

  Not all relationships benefit ants. The fungi Cordyceps and Ophiocordyceps infect ants, causing infected individuals to climb plants and sink their mandibles into plant tissue. The fungus kills the ant, grows on the remains, and produces a fruiting body, apparently altering ant behavior to disperse its spores in the most suitable microhabitat. A nematode called Myrmeconema neotropicum that infects canopy ants of the species Cephalotes atratus turns their normally black abdomens red and causes them to hold the abdomen high, mimicking ripe fruit. Birds eat these ants, and the nematode spreads further through the droppings consumed by other ants.

  A study of Temnothorax nylanderi colonies in Germany found that workers parasitized by the tapeworm Anomotaenia brevis, for which woodpeckers are the definitive hosts, lived much longer than unparasitized workers, with mortality rates comparable to those of queens, which can live for as long as two decades.

• 8. Ants and Human Life

  ›

  In parts of Africa and South America, large ants serve as surgical sutures. A wound is pressed together, ants are applied along it, and each ant seizes the wound edges with its mandibles and locks in place. The body is then cut away, leaving the head and mandibles to hold the wound closed. The large heads of the soldier caste of the leafcutting ant Atta cephalotes are used this way by some native surgeons.

  In Mexican cuisine, eggs of two ant species are used in a dish called escamoles, considered a form of insect caviar that sold for as much as US$50 to US$200 per kilogram as of 2006, depending on availability. In the Colombian department of Santander, a species called Atta laevigata, known locally as hormigas culonas, are toasted alive and eaten. Weaver ant eggs and the ants themselves appear in a Thai salad called yam khai mot daeng from the Issan region of northeast Thailand. In parts of Bulgaria and Turkey, ants or their pupae are used to start yogurt.

  Ultraviolet vision was first discovered in ants by Sir John Lubbock in 1881. Since then, the social structures of ant colonies have made them valuable model organisms for testing theories of kin selection and evolutionarily stable strategies. The techniques used by ant foraging colonies to find optimal paths have inspired computer science approaches including Ant Colony Optimization and Ant Robotics, applied to distributed systems, search algorithms, and fault-tolerant networking.

  The video game SimAnt, which simulated an ant colony, won the 1992 Codie Award for Best Simulation Program. E. O. Wilson, the myrmecologist who had spent decades studying ants in the field and lab, published a short story called "Trailhead" in The New Yorker in 2010, describing the life and death of a queen and the rise and fall of her colony from the ants' own perspective. The Australian jack jumper ant Myrmecia pilosula, which carries only a single pair of chromosomes in its cells, with males having just one, holds the record for the lowest chromosome count of any known animal, and continues to be studied for what it can reveal about the genetics of social insects.