Friday, September 5, 2014

Ant Biology

The Ant Colony

Ants belong to the order of insects known as Hymenoptera, that also includes sawflies, bees and wasps. Some bees and wasps are social insects; ants, at the top of the tree of insect life, are all social (by rough analogy, if these were all primates, bees would be furry lemurs, wasps would be monkeys and ants would be apes). There are no solitary ants.
Ants, in the family Formicidae, are believed to be descended from wasps, and they share many characteristics with them. However, they have many ‘stand alone’ features that all ants, and only ants, share. 
* Because all ants are social, if you find one ant there will always be others from the same colony somewhere nearby.
* Almost all the worker ants you’ll ever see are females. Male ants or ‘drones’ have short, idyllic lives, where they are born, hang around the nest being pampered and fed, and then fly off to find females (‘alates’) to mate with. After mating they are unable to care for themselves, and they die.
* The colony usually has a queen or several queens who do the reproductive work, although there are species of ants where a mated worker or workers may share or take on the reproductive role.
The queen, technically known as a gyne, starts her adult life as an alate, with two pairs of wings which she uses on her mating flight (queens of the Dorylinae, however, are quite different). After mating – and she only mates once in her life – she drops her wings, finds a suitable nesting site and lays her first eggs. The eggs are small and white or sometimes yellow or pinkish. They hatch into blind, legless larvae that are completely helpless, and unless constantly fed and groomed they die. The queen tends these through the larval and pupal stages until the first workers eclose from pupae (eggs hatch, pupae eclose). She uses nutrients from her now-redundant wing muscles to nurture her first brood. The first workers are often smaller and paler than subsequent generations, but once they have eclosed the queen can relax and look forward to a long life (20 years or more, sometimes!) of laying eggs and being fed and groomed by her workers, who take over the gathering of food as well as the care of the eggs, larvae and pupae.
Note that in some subfamilies the larvae spin cocoons, within which they pupate, while in others the pupae are naked. In both instances they have to be helped to eclose by their older sisters, who tear the pupal ‘skin’ and/or silk off the helpless newcomers. Newly eclosed individuals have incompletely sclerotised chitinous exoskeletons and are often pale yellow or grey in colour; they are known as tenerals or callows, while the discarded pupal materials are known as exuviae.
In some genera the workers can also have different castes: minors and majors, dimorphic or polymorphic; and in some cases even ‘intercaste’ sexed or ‘ergatoid’ workers, who can be queens or males.


Ants construct their nests in a remarkable variety of ways. Even the ‘simplest’ hole-in-the-ground nests reveal a remarkable complexity. Experiments pouring (with great care) molten aluminium down ant nests (experimenters insist the nests were unoccupied!) reveal an extraordinary structure, which when carefully excavated can be a thing of some beauty. Chambers are linked by tunnels which often reach a considerable depth.
Hole-in-the-ground nests may have simple hole entrances without adornment, or these might be surrounded by a perfectly circular cone of sand grains brought up from the excavations below. Some ants construct an elaborate vertical turret as their entrances, perhaps to prevent rainwater running into the hole; other ground dwellers expropriate a few floors of a termite mound.
Other ants simply excavate a few tunnels or chambers under stones; some burrow into wood or take over the tunnels left by other boring insects, while others—very thin ants such as Tetraponera (Slender ants)—hollow out the soft interior of Watsonia or Aristea stems to house themselves. The rare Bee-legged boring ant, Melissotarsus, is a true carpenter and bores into the heartwood of certain plants and, once there, never leaves again, living off the secretions of plant-sucking coccids that it introduces into the plant.

The dedicated spinners, Tailor or Weaver ants (Oecophylla), famously use their silk-producing larvae to tie tree leaves together to make arboreal nests.                              Many Polyrhachis, the Spiny sugar ants, also use their larvae to spin cup-shaped walls of silk, grass and soil around their nest entrances, often lining these with silk for some distance into the ground.
Messor ants, seed harvesters, often create a ‘midden’ of chewed up vegetable matter around their nest entrances; if this is undisturbed for long enough it may become bound into mounds by vegetation—or it may all blow away in the next strong wind.
Their cousins, Myrmicaria or Droptail ants, leave similar mounds of detritus around their entrances, occasionally moulding the mixture of dead stuff and soil rather crudely into entrance mounds or even tunnels. Monomorium fridae, the vicious Frida’s fierce timid ant, builds similar detritus mounds which it defends vigorously with tooth and sting.
A different kind of earthen-and-stick mound is built by the Hairy sugar ant, Camponotus niveosetosus. Uniquely in the genus, it constructs these nests in reedy tussocks in wet, marshy ground, where the nest material  becomes bound together by mossy or fungal strands.
Camponotus bianconii builds carton-like chambers under the loose bark of dead trees, very similar to the carton produced by Cocktail ants, Crematogaster spp. These build unique nests of chewed up-vegetation glued together with their own saliva. The result resembles crude brown papier maché. The nests, that may house hundreds of thousands of ants, can be high up in bushes and trees or low down around the base of shrubs—but never on the ground. How they survive fire in fire-prone vegetation is one of the unsolved mysteries of the ant world.
And then there are a few—just a few, but famous— species that nest in the hollow thorns and galls on trees, where they may help defend the tree by vigorously attacking any browsers who should incautiously push noses and tongues too close.

ANT BIOLOGY: Ant Behaviour;  Ecological Role of Ants

In 1925 the South African naturalist and poet Eugène Nielen Marais published a series of articles in Huisgenoot magazine titled ‘Die Siel van die Mier’ (‘The Soul of the Ant’, often misquoted in English as ‘The Soul of the White Ant’.) The articles were shamelessly plagiarized in 1926 by the French Nobel Laureate Maurice Maeterlinck*, who should have known better, in his La Vie des Termites. Marais also put forward the hypothesis that the termite colony was in effect a single organism. This concept was also pinched by Maeterlinck and, more recently, has even appeared in the work of Richard Dawkins. But what has this got to do with ants?
[* The poet Stephen Gray has tried to debunk this by suggesting that Marais in fact stole Maeterlinck’s ideas—but I ask you, how could a rural Transvaler pre-publish by one year the manuscript of a French professor who in fact admitted that he had never seen a termite in his life? Steve surely forgot that there was no fax/email/internet in the 1920s, a somewhat anachronistic error of judgement ...]
The first problem was Marais’s title. I’d be a rich man if I had a dollar for each time that people, hearing that I am interested in ants, have winked and said, ‘Ah! The soul of the (white) ant!’ A comprehensive inability to distinguish between termites and ants has apparently been engraved on the human genome ever since, and, I’m sorry, Marais, all his imitators and his subsequent book (on the right) are absolutely to blame. 
The second problem is the proposition that the termite colony is a single organism. The idea may seem to have merit, even when trans-ferred to ants and bees, but it has unfortunately led to a proliferation of very problematic, quasi-mystical ideas about collective intelligences, ethereal souls, and evidence of the Hands of Sundry Deities—all gushingly described in the muddier recesses of the internet.
Marais was writing decades before pheromones were discovered. First identified in 1959 and present in all animal phyla including humans, pheromones are chemical substances that you secrete in various ways and that consequently influence the behaviour of your fellows. Ants and other social insects use pheromones to maintain colony unity. Recognition pheromones help ants to tell friend from foe; ants in the same nest constantly tap each other with their antennae, detecting these ‘friendly’ pheromones. If an enemy is detected ‘attack’ pheromones might come into play, and these stimulate other ‘friendly’ ants to join the attack.
Trailing behaviour in many ant species is also pheromone-driven. After a foraging ant has found a food source she returns to her nest, frequently tapping her gaster on the ground and thus marking the route to the food with a pheromone. The particular pheromone triggers a ‘move towards me’ response in other ants, and in no time a trail to the food source develops. Each individual on the trail constantly reinforces the pheromone markers. As the food declines fewer and fewer ants use and mark the trail, until eventually the pheromone has evaporated, no ants are renewing it, and the trail disappears.

Not all ants exhibit trailing behaviour. Many forage individually or in pairs; others such as harvesters who collect randomly-fallen seeds from all over the place, might come together near the nest in a vague trail. As a general rule ants that live in larger colonies—perhaps from many thousands of ants rather than several hundreds—are more likely to ‘trail’ than those in smaller.

        Pheromones similarly guide most ant behaviour, from the treatment of the queens and the brood to defence of the colony. The individual ant is not really capable of making any individual decisions, nor does the queen radiate some sort of mysterious, ethereal bonding vibe—her pheromones smell, that’s all.
Trophallaxis is another important process that binds the colony. Most highly developed in social insects such as ants, termites, wasps and bees, this is the mouth-to-mouth transfer of regurgitated food—essentially fluids—from one individual to another. Ants use a particular pattern of antennal stroking to induce a fellow ant, or a queen or a larva, to accept their regurgitated droplet of nectar. Other patterns are used by hungry ants to induce regurgitation from another that has filled her stomach. In many ants a further process has evolved: some individuals get fed and fed and fed until they swell up into living storage vessels—the so-called ‘honeypot ants’, whose store of nectar can be tapped at any time by antennal manipulation.
Although I read somewhere that this complex process was proof-positive of the theory of creationism (but why?), it’s clear that in social animals that don’t have hands other ways have evolved to carry food to their friends and young. Many non-social birds or mammals regurgitate food for their young, too.
Ants have evolved a variety of ways to deal with threats to the colony. These might come from ant-eating mammals, ant-eating ants, or various other sources. The ‘attack’ pheromone is freely used and results in instant action. Once activated, ants use their mandibles (biting is the most common form of defence/ attack in most animals, after all!), but they might also use stings (Ponerinae, Myrmicinae, etc), chemical repellants (Dolichoderinae, many Myrmicinae) or, amongst the Formicinae, powerful sprays of formic acid from the ‘acidophores’ which they have instead of stings. Ants are usually, but not always, fiercely antagonistic towards ants of other species, and very frequently just as antagonistic towards ants of the same species. It might be ‘nest smell’ caused by subtle differences in pheromones from one colony to another that triggers these responses.
Ants reproduce their colonies in two main ways:
1. By nuptial flights. The alate (winged) females and males fly out of the parent nests and, using pheromones, they attract the opposite sex from a different colony, and they mate. The male dies; the new queen drops her wings and finds a sheltered place for her new colony. She lays a few eggs and when these hatch she raises them to become her first workers. She does not eat during this time, living off the fatty reserves supplied by her now-redundant wing muscles. Nests established in this way are highly nationalistic and usually hostile to all other ants, including their own species. The whole nuptial flight process is extremely dicey and the chances of failure are extremely high. 

2. By budding. There is more than one reproductive queen in the nest. When a good food source is discovered, some of the extra queens migrate out with the workers and start a new branch of the colony at the food supply. The colony remains interlinked and its members are accepted by all branches. The colonies can grow into enormous super-colonies spread out over many miles, and with countless trillions of individuals.
Humans are always and inexplicably drawn to the bizarre, but I’m sorry to say that some of the weirdest forms of ant behaviour, such as chain gangs, river rafting, slavery, suicide bombing and vampirism (where ants suck the ‘blood’ of their own larvae) are not, as far as we know, found in our region.

Ecological Role of Ants

It has been estimated that although ant species comprise only about 2% of all arthropod species, they nevertheless make up some 30%+ of the terrestrial arthropod biomass—and 20% of the terrestrial animal biomass on planet Earth. Their numbers are uncountable and they are present on every continent except Antarctica. In some areas their nests are so extensive that their role in aerating the soil is more effective than earthworms.
As part of the food web, ants are important cleaners, consuming and recycling tons of decaying plant and animal material. They are massively important controllers of various insect ‘pests’, including flies, termites, etc. Not only do they eat a wide variety of living and dead organic material, they themselves are food for a huge variety of other creatures.
On a regular basis, ants are eaten by:
* Other ants. There are many specific ant predators of ants across a range of subfamilies, ants who take advantage of superior numbers or superior attack mechanisms to exploit the rich resource created by their distant relatives.
* Spiders. There are many spiders who imitate ants, and many of these use their disguises to capture and eat ants.
* Ant lions and ant-worms. Few can be unfamiliar with the conical craters made by these voracious ant-hunters, natural pitfall traps from which there is no escape for the unwary ant.
* Robber and other beetles. There is a wide variety who are specific ant hunters; there are ant-eating mantids, too.
* Reptiles and amphibians. Many lizards, skinks, frogs and toads eat ants. Curiously, despite extensive observation, I have never seen chameleons take ants.
* Birds. Huge numbers of ants are eaten by birds. If you have a bird feeder in your garden, check if there are ants around the feeding tube. If so you may see white-eyes, weavers, bulbuls and even sunbirds picking off the ants.
* Mammals. Most mammals that eat ants are specially adapted, such as aardvark. Analysis of the stomach contents of dead aardvark has revealed that their favourite food is Anoplolepis ants, not termites, as was once thought. Less specialised feeders such as baboons will readily turn over stones and consume the ants’ brood—larvae and pupae—that they find there. Honey badgers are also major consumers of ants. 
Humans who inadvertently consume ants, e.g. on that piece of cake left out overnight, usually spit them out at once. That sharp taste is caused by the formic acid that all ants contain in their bodies—but is in fact quite harmless.
* Plants. Our wide variety of sundews certainly consume a fair amount of ants, whose empty shells can often be found sticking to their leaves.
Ants are of course famous ‘farmers’ of coccids and aphids, insects that convert plant juices into nectar that is regularly ‘milked’ by ants from these economically-important, destructive pests. Some ants even practice a sort of animal husbandry, where they bite off the wings of winged aphids to prevent them escaping; some can even secrete chemicals that prevent the regrowth of wings, or that make the aphids tamer and more amenable to manipulation. The ants also guard their ‘cows’ against predators like ladybirds; they build shelters over them too, though these may be more for the ants’ own benefit.
Some ants are farmers of a different kind, collecting suitable plant material that they mulch within their nests and then sow with fungal spores, producing unique fungal food for the colony. Others are direct predators of seeds of a wide variety of plants, and such species often have majors with massively-powerful jaws that act as living nutcrackers, to crack open tough seed casings.
Another well-known interaction with plants is performed by ants that live in the thorns or galls of certain Vachellia (= Acacia). When browsers tug on the plants the ants swarm out and attack the intruding tongues, or even the soft membranes in elephants’ trunks.
Finally, in our very own fynbos, some ants are directly responsible for the distribution of seeds of over 1200 plant species, a process known as myrmecochory (‘carried by ants’). The nut-like seeds have a sweet, fatty attachment called an elaiosome that imitates the ants’ attractant pheromone. The ants find the seeds and drag them into their nests, where the elaiosomes are consumed. The hard, smooth nutlets, which cannot be gripped by the ants’ mandibles, remain safely underground in the nest until germinated by the passage of the next veld fire. Some fynbos rarities, long thought to be extinct, have reappeared more than fifty years later thanks to seeds which have survived underground in ant nests.
The latter process is threatened by invasion by trail-running ants. Trail-runners such as Argentine ants, some Pheidole, Technomyrmex, Lepisiota species, etc. do not carry food-objects into their nests; they consume them where they find them, taking the juices home in their stomachs. The seeds are left lying out in the open, to be predated by rodents and birds, or destroyed in the next fire.

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