All about ants, brainy ‘Supermen’ of insects

0

Ants can lift up to four-and-half tons over their head and run at 52 miles per hour, relative to body size!1 There’s even one species—sort of the Usain Bolt of the ant world—that can run at the human equivalent of 400 miles per hour! But, there’s more to ants than just vigor and brawn—they manage cities and farms and have the largest brain-to-body weight of all animals. They’re fascinating, and you’ll uncover many more interesting facts as you learn all about ants.
Jump down to: Beneficial,  Background  •  Physical description  •  Head, Mouth, Antennae, Brain  •  Senses, Pheromones, Communication  •  Thorax, Appendages  •  Abdomen, Heart, Organs, Breathing  •  Eusocial, Castes  •  Reproduction, Eggs, Larvae  •  Nests, Anthills, Bivouacs, Sleep  •  Foods, Predators, Defenses, Lifespan 

Ants are beneficial

You’ve probably noticed the whirl of activity that always surrounds ants, but what are they accomplishing, other than stealing our tasty picnic foods? Well, quite a lot, really—they’re among earth’s beneficial wildlife, and here’s why:

  • Some ants prey on other insects and their eggs, which helps to control pest populations.
  • Their tunneling in soil aerates it, allowing water and nutrients to penetrate down to plant roots. “Tunneling ants turn over as much soil as earthworms do,” according to FineGardening.com.
  • They disburse seeds.
  • Ants protect nectar-producing plants from herbivorous insects.
  • Ants themselves are food for other beneficial wildlife.

Background

Ants have a long history. Fossil evidence shows they’re evolved from a lineage of stinging wasps and have existed for at least 92 million years (since the Cretaceous Period). It’s thought their longevity is related to a high level of social organization, which helped them adapt to environmental changes through the ages.

Respected sources vary as to the number of ant species in the world. It’s anywhere from 8,800 to 12,500,1 but all agree there are many more awaiting discovery. Ants are found nearly everywhere, except for Antarctica and some islands. In North America, there are about one-thousand species. Ants of N.A.

Ants are called “eusocial” insects, which means they live in highly organized colonies that vary in size from dozens to millions of individuals. A supercolony found in Japan had an estimated 306 million workers and one million queens living in 45,000 interconnected underground nests! Overall it covered 670 acres (271 ha). 

The word “ant” derives from Old English æmette, the German word Ameise, plus a compound of other word forms. It means “the biter off,” perhaps a reference to their biting habits. They belong to the taxonomic order Hymenoptera (hymen-AWP-ter-uh), along with bees, wasps, and sawflies. Ants, wasps, and sawflies (but not bees) are further classified into the family Formicidae (form-uh-CID-ee).2

Physical description of ants

Ants are invertebrate animals (yes, animals, as they fit all the definitions of that). They have a hard, protective skeleton made of chitin, the same material that forms our fingernails. Unlike humans, however, it’s on the outside of the body and called an exoskeleton. 

Species vary widely in size, from 0.030 inches (the length of a grain of rice) up to 2.0 inches (0.75 to 52 mm). The largest in the world are probably eight South American species belonging to the genus Dinoponera, which measure from 1.2 to 1.6 inches long (3 to 4 cm). The smallest are likely those in the genus Carebara, which are found worldwide. In North America, the Black Carpenter Ant, Camponotus pennsylvanicus, is probably the largest, and measures about 0.5 inches long (1.25 cm). As for coloration, most ants are brown, black, or red, but a few species are green, and some tropical species have a metallic look.

Ants have three main body sections—head, thorax, and abdomen.

Head

The ant has two large, dark, compound eyes and three simple eyes called ocelli (oh-CELL-ee), which are grouped as a triangle near the back of the head. The former detect movement, while the latter discern light and polarization. Two moveable antennae with elbows are attached to the front of the head; they’re used for smell, touch, and feel, and to communicate with other ants.

Ants have two strong mandibles (jaws) with teeth that are used for cutting, carrying food, nest construction, fighting, and digging. Mandibles vary in shape, according to species. There are separate  mouthparts for chewing food. Several body parts—labial glands, nerve ganglia, and the esophagus—begin in the head and extend into the thorax and abdomen.
Close up of an ant queen's head.

Head of a queen ant. The two projections are her antennae. (Roverhate / Pixabay; PD)



Brain

Entomologists have long accepted that the collective intelligence of an entire colony is what imparts intelligence to each of its members; in other words, an ant without a colony is clueless. An ant brain is mainly a bundle of nerves and fibers and consists of only about 250,000 cells (for comparison, humans have about a hundred billion).

Recent research, however, is flipping this belief on its head, so to speak, showing that ants are very smart as individuals. They’re capable of processing complex data, storing information, taking advice from other ants, and are altruistic toward each other. And, when a colony picks up and moves, it’s led by its most intelligent members. Some ant species have 14 to 15 percent brain mass compared to body weight, the highest of all animals!

Senses and communication

Ants have five senses: touch, smell, taste, hearing, and vision.

Touch: If you observe them closely, you’ve noticed that ants touch each other with their antennae. That’s an important form of communication for them, used to convey through pheromones such information as who they are and where they’ve been. Ants can also feel through tiny hairs on their body when touched.

Pheromones and smell: There are pheromone glands throughout the ant’s body, and they’re very specific. For instance, these chemical signals can mark a trail for others to follow to a good food source. An injured or crushed ant will emit a pheromone that triggers alarm. Pheromones are also secreted to mark territories, mark the way to new nest sites, and trigger sexual behavior. A single trail may consist of several different pheromones from one or more glands.

Recent research has shown that trail pheromones are remarkably sophisticated. The provide information about previously used trails, current trails, and unrewarding branches. Also, there’s worker specialization in laying trails and the detection of them.

The antennae play an essential role in the sense of smell. They contain four to five times the number of odor receptors of most insects and are used to detect food. Research shows these receptors are so keen they can distinguish between two molecules that differ only slightly.

Taste: An ant’s sense of taste is closely linked to its sense of smell. They don’t have actual taste buds, but taste receptors located in the mouth and the chemical odor receptors in the antennae combine to give them a sense of what something “tastes” like.

Hearing: Ants don’t have ears, but they can “hear” by feeling and interpreting vibrations through different body parts, such as their legs and antennae.³

Vision: This is the least important sense, even though ants seem to have an over-abundance of eyes. Their two compound eyes are comprised of many singular units. Each unit, called an ommatidium, has its own tiny field of view. The nervous system combines all of them to produce a complete picture. However, it’s a blurry one. The ant’s three simple eyes each have a single lens, but they’re fixed and don’t adjust for close up and distance. Still, ants see well enough to navigate even the most challenging terrain. (A few subterranean species are blind.)

Thorax

The thorax is the middle section of an ant’s body. Six strong, jointed legs, three on each side, are attached to it. At the end of each leg are two hooked claws and a dense array of fine hairs, which are used for gripping surfaces and other ants.

On their feet are pads that can stick to vertical surfaces. How? The secret is that the pads are wet and create a strong surface tension between a foot and the surface it’s on. The ant un-sticks by folding its foot up. (A good comparison is when surface tension causes a wet glass to stick to a coaster, but tilt it slightly, and it releases its hold.) Asian Weaver Ants (genus Oecophylla) create such strong surface tension they can walk across glass upside down while carrying up to one hundred times their body weight!  Video of Asian Weaver Ants and how they do it

Drawing of the anatomy of an ant, with labels.

Anatomy of an ant. (Mariana Ruiz / wiki; PD)



Extending into the thorax from the head are the esophagus, labial glands (which aid in digestion) and nerve ganglia (which supply commands to the legs and wings, and interpret sensory input from the eyes). Between the thorax and abdomen is a node that looks like a waist. Called a petiole, it’s another digestive aid, and has either one or two segments, depending on the species. (This physical feature helps taxonomists identify ant subfamilies.)

Color illustration of internal anatomy, showing the glands.

(Cronodon.com; cc by-nc-sa 3.0)



A
bdomen

The ant’s largest body section is the abdomen. It contains nerves, vital organs, including the “heart,” part of the digestive system, and reproductive organs.

Heart: Ants don’t have a heart as we know it. Instead, the dorsal aorta, a pump of sorts, takes its place. Its job is to move blood to the ant’s head. From there, blood washes backward through the rest of the body. There are no vessels involved—it floods around the organs in what’s called an open system.
Reproductive organs: Queens and worker ants (who are always females) have egg-laying tubes. The tubes run from the front of the abdomen to the tip. Typically, only the queen has fertilized eggs, though, which she stores in little sacs. Many species, but not all, have modified tubes with a stinger at the tip. The stinger contains a poison gland that holds formic acid,2 a strong irritant—this is what gives fire ants and others their painful “fire.” Also, at the tip of the abdomen is the Dufour’s gland, which secretes a pheromone used as a trail for other ants to follow.

Respiration: Ants don’t have lungs to pump air in and out. Instead, through a process called rhythmic tracheal compression, they breathe passively through a series of tiny pores located on their body. Called spiracles, they attach to tube-shaped trachea that grow narrower and narrower as they network through the body. As the ant moves, it draws air in and out.

Learn more about insect anatomy    

Eusocial living

Ants, along with various bees, wasps, and termites, are called “eusocial” because they live in a cooperative group that organizes work efficiently by dividing tasks and sharing information. This behavior seems to give them an advantage over solitary insects. For example, by sharing, ants can convey to each other the shortest distance between two routes to get to a good food source.

It’s commonly thought that ant colonies have only one queen, but, depending on the species, there may be more. Or none: Some colonies, called gamergate colonies, have no queens, and all the workers there, called gamergates, are females capable of reproducing. Usually, only a few among them do, however. In colonies that have more than one queen, one of them might leave with some of the workers to form a new colony.

Castes in an ant colony

Queen, soldier and worker Big-headed ants, Pheidole californica, in their nest.

Big-headed Ants, Pheidole californica, in their nest, showing queen, soldier, worker, and larvae. (Alex Wild / Wiki; PD)



Typical ant colonies have at least three kinds of ants—a fertile queen, fertile males, and non-reproductive females called workers, but some species have additional castes of workers.

  • Queens spend their entire lives laying eggs; it’s their only role.
  • Males have only one job, to mate with the queen.
  • Workers do everything else in a colony and are assigned specialized jobs. The smallest ants, called minor workers, find and gather food; clean, maintain and expand the nest; feed and care for the queen; and care for eggs and young offspring.
  • Major workers, sometimes called soldier ants, are larger and stronger than other workers. They have a large head with powerful jaws designed for specialized tasks, such as seed-cracking, wood-boring, or combat.
  • Median workers fit, in size, between major workers and minor workers and also perform tasks to support the colony.²
Extreme close up of an ant, clearly showing the many facets of its compound eyes.

Extreme close up of an ant, showing the numerous ommatidia of its compound eyes and hairy body. (Retro Lenses Wikimedia cc by 4.0)



Reproduction

The lifespan of an ant involves a process called complete metamorphosis, which means it progresses from an egg to a larva to a pupa to an adult.

It all begins in late-spring to early-summer when fertile virgin queens and males simultaneously leave their existing colonies in vast swarms called “nuptial flights.” They all have wings and are able to go their own way. Far away, in fact, where they’ll mate (in the air) with ants from different colonies, which prevents inbreeding. Males die soon after mating, having completed their role in life.

After mating with one or more males, the queen flies off to find a suitable nesting site. There, she drops her wings, which fall to the ground, never to be used again. Her task now is to construct a nest.

A young, fertilized meat ant queen, genus Iridomyrmex, excavating a hole in the ground for her nest. (Fir0002:Flagstaffotos/wiki/GFDL 1.23)



Depending on the species, it might be underground, in wood, walls, cracks in the pavement, nearly anywhere that’s suitable for a long tunnel with a small chamber at the end. She usually excavates the tunnel alone, then seals herself in the nest and lays eggs. Then, again—queens sometimes wait until the following spring. Either way, she’ll raise her first group of workers alone and stay in total darkness for the rest of her life, unless her nest is damaged. (Queens of some species cooperate and raise the first brood together. If this occurs in a species that’s ultimately to have only one queen to a colony, called monogyny, the once-cooperative queens will fight to the death of one of them.)

Eggs, larvae

The young queen feeds salivary secretions from her mouth to her first brood. She doesn’t eat during this time. After her first workers are grown, they take over the care and protection of all following eggs and larvae.

An ant egg is about 0.02 inches (0.5 mm) in diameter and weighs about 0.0005 grams. It’s kidney-shaped and sticky, which bonds it to other eggs. This allows adults to carry many stuck-together eggs at once, a big help in an emergency.

A larva hatches in five to seven days and looks like a tiny maggot. It doesn’t have legs, but it can move minimally. At first, it’s fed juices made from soft, regurgitated food and later on, solid foods. It sheds its skin (molts) each time it outgrows it. It also gets hairier. Some of the hairs are hooked at the end and can lock to other larvae—this enables workers to carry several at a time, when necessary. At the last molt, larvae are too large to be carried as a group.

Image of a male Carpenter Ant with wings.

Winged male Carpenter Ant, Camponotus castaneus. (Katja Schulz / Wiki; cc by 3.0)



Haplodiploidy

The queen can control the sex of her offspring. In a reproductive process called haplodiploidy, she can lay unfertilized eggs, which become males, or fertilized eggs, which become females. Or, she may choose to store fertilized eggs in her “sperm pocket” (spermathecae) for use soon or in the future. She holds enough sperm in her body to last her lifetime and will fertilize millions of eggs. When a queen stops producing a specific pheromone, it signals to the workers that it’s time to start raising new queens.

Nests

An ant nest is where a colony lives. It may be located underground, in wood, under stones, in mulch or debris, in walls or mounds of soil. Gardeners find nests under or in flowerpots or even within a water hose left unused.

Small golden-colored anthill located between two paving stones.

A nest is below the paving stones. (© S1001 / Shutterstock)

Pavement Ants, Tetramorium thicaespitum, typically nest in or under cracks in pavement or foundation walls. Wood ants, Formica sp., nest in masses of pine needles on top of old tree stumps or on the ground. Acorn ants, Temnothorax sp., nest inside acorns, as well as walnuts, twigs, and other small cavities. Ants in the genus Oecophylla use silk to weave leaves into nests.

A nest is a highly structured network of chambers connected to each other by tunnels. Some chambers are nurseries, others are used for food storage. Ants in a German study in 2015 even set aside some chambers as “bathrooms.”4 Nests begin small and expand as the colony grows bigger. Corridors and chambers may interconnect for vast distances. A nest found in Australia in 2004 measured 62 miles (100 km) wide, most of it underground. Some underground nests may trail down 26 feet (2.7 m)

Belowground structure of a Florida Harvester Ant.

Belowground nest structure of a Florida Harvester Ant. (Shaners, Becker / wiki; cc by-sa 2.0)

Anthills

Anthills are formed from the excavated soil and debris that ants carry from belowground as they dig tunnels and chambers. Generally, it’s deposited in a circle around the entrance hole. You’ve probably seen these “volcanos” in your own yard.

Ant bivouacs

You may have heard of ant “bivouacs,” which are temporary camps. They’re made up of army ants (over two hundred species in several genera), who defy custom by not building permanent nests at all. An entire colony travels continuously in search of food. When the ants come to a halt, they link their bodies together until they’re ready to travel again.

Sleep

Considering the heavy workload of ants, they need some rest. A 2009 University of Florida study of fire ants showed that each worker took an average of 250 one-minute naps a day. Nap times were staggered, so some workers were always awake while others slept. Queens took about 90 six-minute naps a day, and they dream.

A mass of hundreds of Army Ants ilinked to each other in a bivouac.

Army Ant bivouac. (Geoff Gallice / Wiki; cc by 2.0)



Foods

Ants are opportunistic omnivores. Scavengers, rather than hunters, they eat what they come across. In general, they feed on soft-bodied animals, such as mites and other spiders, the larvae of other insects, and carrion. Species in some parts of the world eat seeds or fungus. Ants also eat sweets found outdoors or inside—candy, honey, fruit, and jam—which provide carbohydrates for energy.

Three ants on a plant stem with a group of green aphids.

Worker ants tending to their herd of aphids. (© Ed Phillips / Shutterstock)



Many ant species maintain herds of aphids, because they like a sweet solution secreted by them, called honeydew. In return, the ants protect their “livestock” from predators! Look closely if you see a group of aphids on your plants, and you may spot some ants tending to them.

Predators

Predators of ants are birds; lizards; some species of spiders; other insects, including other ants; armadillos, anteaters; and Aardvarks.

Defenses

Ants have several defenses. They can bite, and some can sting. The sting of the Bullet Ant, Paraponera clavata, a large Rainforest species, is worse than any other ant, wasp or bee—according to some human victims, its sting is equivalent to being shot (hence its name). Ants can use other tactics, too, like blocking the entrance to their nest with their heads (a process called phragmosis) to prevent enemies from entering. The Fish-hook Ant, Polyrhachis bihamata, another Rainforest species, has sharp spikes on its back, which can be used to interlock with other ants to prevent one of their colony from being dragged away. They also use them to stab enemies.

Lifespan

Queen ants may live up to thirty years, the longest span of any known insect. Workers live from a few months up to five years. Males die soon after mating.

* Top photo: Charlie Stinchcomb / Wiki; cc by 2.0
1 National Geographic says “more than” 10,000. Animal Diversity says 8,800, Britannica.com says “approximately” 10,000, Wikimedia reports “more than” 12,500.
2 “Formic” comes from the Latin word for ant, formica. Formic acid, which was originally distilled from ant bodies, is now produced through chemical compounding. It’s primarily used by industry as a preservative and antibacterial agent.
3 GDFL License Documentation   
4 Ant bathrooms

More reading

About specific ant species 
More about eusocial insects and communication  
A fun and interesting read: 7 Reasons Ants Will Inherit the Earth

Learn also about spiders, termites:

Spider magic: silk, spinnerets, webs, and spiderlings   
All about termites   

Share.