|Insect Societies - tribal kinship and foreign policy
|See also: Introduction to insect behaviour and control systems; the insect brain.
Above: a red ant (a Povray model of a formican ant). Many insects associate in large numbers and
individuals in such associations may communicate and work together, as in locust swarms and beetle
colonies. However, fully social, or eusocial behaviour, only occurs in bees, wasps, ants and termites.
(Though highly social behaviour can occur in some other arthropods, such as certain spiders that form
social nests). Of these insects, all except the termites are hymenopterans (family Hymenoptera) whilst
termites are dictyopterans (the family Dictyoptera includes termites, mantids and cockroaches).
However, not all bees and wasps are social, some are solitary, whilst others form small nests where the
mother cares for her offspring. From these intermediate stages, it was a relatively short step to the
evolution of large societies, in which the children continue to care for the mother, or queen, who
continues to lay more eggs. This was accomplished by an elongation of the mother's lifespan, with
termite queens living as long as 20-50 years.
In an ant colony, most of the individuals are sterile females that will never be able to have children of
their own, and yet they will work, fight and die for their colony. What engenders such 'altruistic' loyalty?
Darwin considered this a key problem in his theory of evolution - why would an animal evolve so as to
throw away its own chance to reproduce if it is survival of the fittest? His answer was that evolution must
act, not on the individual, but on the group as a whole. This group selection is a controversial theory,
and probably has some truth in it, however, kinship provides a stronger selective force. The sterile
workers and soldiers of a nest are all sisters. This means that any two sisters share 75% of their genes
with one another and 50% with the queen. Evolution acts ultimately upon the genes as only genes
survive from generation to generation. Thus, a gene can facilitate its own survival by helping other
copies of itself to survive, it would even profit a gene to sacrifice one copy for the sake of two or more
copies. The closer two animals are related to one another, the more of their genes that will be alike, so,
genes ensure the survival of their own copies by programming an animal to behave altruistically toward
its kin, and the closer the kin, the stronger the altruism. This is why humans (usually) cherish their own
offspring above other people - not for moral reasons, but for the sake of gene survival (sorry)! The way
evolution acts to favour kin in this way, is called kin selection.
In humans, siblings share 50% of their genes in common, but ant, bee or wasp nest-mates are even
closer than this, so evolution has favoured the development of strong social bonds in these insects.
Interestingly, because of the way hymenopteran genetics work, males share only 25% of their genes
with the female workers, and so males are often not treated as well and are only produced to
inseminate virgin queens after which the males die! Note also, that the queen is cared for only because
she produces more siblings for the workers, so the hierarchy works both ways!
Professions and Social Castes
Bees and wasps have only a few morphological types within the same nest (although there are many
varied species) - the queen, male drones and sterile female workers. The workers adopt different roles
as they mature. Early on in adult life a worker bee produces royal jelly to feed developing bees and
young queens. The bee will also switch to other tasks such as building wax cells. After about 3 weeks
after emerging from its pupation cell, the worker then begins to forage, which is a hard job and the bee
eventually dies from wear and tear (after about one month). Thus, the same individual performs
different tasks according to its age. This is division of labour.
Division of labour is key to any organised collective. The many cells in your body work closely together
(they are genetic clones sharing 100% of their genes with one another, so kin selection has had a
strong effect in producing multicellular organisms like you) and they divide tasks between themselves -
you have nerve cells, muscle cells, bone cells, skin cells, etc. Similarly in human society, different
people perform different tasks for which they are more or less specialised. However, there are few
morphological differences between human social groups, although the old adage that a man's muscles
betrays his profession (a archer, for example, had a very well muscled left arm if he was right-handed)
shows how humans can adapt through training and experience. This is more evident, of course, in
terms of manual and intellectual skills.
Ants and termites show extraordinary adaptations to the various tasks each is alloted to. Worker ants
are usually small, though well adapted to lifting and manipulating objects with their mandibles and front
legs. Soldier ants are better armed and are often larger with tougher armour and stronger fighting
muscles. The queen has an enlarged abdomen, grotesquely bloated in termites, for egg production.
Some ant and termite societies even have different types of workers or soldiers. In termites, special
large soldiers may act as a last line of defence for the royal couple. The Asian army ant, Pheidologeton
diversus, have special individuals ten times the normal size, whose task it is to remove heavy obstacles
from the path of raiders, working like bull-dozers with their enormous strength and large clasping jaws.
In Atta leafcutting ants, small gardeners, 3 mm in length, raise fungi in special gardens, whilst the
largest soldiers may be more than 2 cm in length! The appearance of different body shapes, or
morphs, is called polymorphism. There is little hierarchy in these societies, in the human sense, workers
are not treated with contempt (!), rather each individual has its important role to play and plays it
according to programmed instinct.
This division of labour, with each individual acting rather like a cell in a multicellular organism, has led to
the adoption of the term 'super-organism' to describe insect societies. However, this analogy only
stretches so far, since ant sisters only share 75% of their genes, not 100%, so even in these societies
there can be elements of selfish behaviour, albeit not as pronounced as in human societies bound by
weaker genetic similarities!
When considering ants in particular, it seems that foreign affairs are of the utmost importance. It is
estimated that the total mass of ants on Earth equals the total mass of human beings! Indeed, in the
Amazon rain forest, the total mass of ants probably exceeds the total mass of all the vertebrates (frogs,
reptiles, mammals, birds, etc.). Ants are probably the most successful of all the insects. With so many
ants competing for resources, it should be no surprise that ants excel in the art of war! They are
probably the most aggressive animals on Earth! This is not to imply that ants get 'angry' but simply that
war is a natural part of their instinct and daily lives, although this depends upon species, with some
being much more aggressive than others. So it is, that ants frequently make war upon one another, and
Ant and termite weaponry
To live by the sword! The most fundamental weapons are crushing jaws. Worker ants and termites may
use their jaws for carrying and lifting, but soldiers may have jaws especially modified for crushing
enemies! These stout jaws use large muscles in the head to simply crush the limbs of an opponent and
to pierce enemy armour. In many cases, however, the jaws have adopted a more advanced design that
saves on muscle power - they may be designed with sharp piercing points, or they may become
slashing blades that swing from side to side like reaping scythes, often crossing over one another. The
large soldier ants of Pheidole dentata can snip heads and limbs off smaller fire-ants with their sharp
jaws! This is just as well, since they must dispatch fire ant scouting parties very quickly, since if any
escape to report to headquarters, the fire ants will over-run the Pheidole nest with a combination of
huge numerical advantage and deadly stings. Behaeding, by the way, is not always a quick death for an
insect - the separated head and body may go on living and moving for hours or days, before
dehydrating! Snapping jaws press together, building a charge of energy that is stored in their elastic
cuticles, to be suddenly released with a click, knocking into an opponent with tremendous kinetic
energy. The Capritermes group of termites have elastic jaws that are asymmetric and can only snap to
the left, but which are capable of disabling an enemy ant in a single blow!
Projectile weapons and chemical warfare! Ants are close relatives of the wasps and many ants retain
their venomous tail stings in addition to possessing fierce mandibles. In the formican ants, the sting has
been replaced by a nozzle that sprays venom or acid onto opponents at range! Termites are related to
cockroaches and so have no sting in their tails, however some termites, like Nausitermes, have done
away with jaws and have head-mounted cannons that spray irritants, toxins and/or glue to disable or kill
ant attackers. The termite, Acorhinotermes, has a paint-brush (a modified labrum) mounted on its head,
which far from being as inoffensive as it looks, paints contact poison upon enemy ants. Termites
typically have built-in antidotes to their own poisons whilst their glues only become viscous and sticky
on contact with air and entangle their opponents. Many of the crushing, piercing and slashing weapons
of termites also deploy toxic or irritating chemicals into the wounds they cause!
Phragmosis is a second line of defense used by termites, which employs special soldiers. These
soldiers guard key passages into the nest. These passages narrow to a diameter that is exactly
plugged by the very tough and large shovel-like heads of these soldiers. In front of this are powerful
slashing jaws! Ants forced to file through these narrow passages, seeking to over-run the vital parts of
the termite nest, must face these juggernauts head-on, one by one! This reminds me of the book,
Fantastic Planet, in which brave warriors attacking the evil citadel become funneled through a narrow
passage which opens out abruptly into a chamber containing a giant ogre wielding two giant scythes!
The warriors, pushed into queue, have to face this grim opponent one at a time! Needless to say, many
die before the ogre is finally slain.
Self-destruct mechanisms! Many termites employ workers to assist their soldiers in battle, as a matter of
course for some species that may have few or no soldiers at all, or as a last resort, or as skirmishers.
The workers of some termites will line up, then defecate noxious chemicals on their opponents, before
retreating and leaving the soldiers to hold the line. In some, the workers have crushing mandibles. This
is a compromise that can work, but it is a compromise - workers have soft bodies, ideal for squirming
through rotting wood and the like, and their mandibles must be able to carry materials and feed the
insect, so they cannot be too specialised. However, workers make up the vast majority in numbers and
so they make a good defence. In Pheidole ants that are over-run by fire ants, the workers may fight at
first, and then retreat to collect and rescue the larvae, eggs and pupae and carry them off to safety,
leaving the professional soldiers to hold the line and fight to the last. This reminds me of how Saxon
armies worked in the Battle of Hastings in 1066 - the farm labourers formed the fyrd which made up the
bulk of the armies numbers. These men were lightly armed and not being professional soldiers they
routed when things got tough, attempting to rescue their baggage train. In the meantime, the
professional soldiers, the huscarls, stayed and fought until dusk, fighting to the death, as was their
sworn commitment once their lord, King Harold, had fallen. Of course, ants do it because their instinct is
programmed to, rather than for any emotive sense of loyalty (presumably).
How does this relate to self-destruct mechanisms? Well, many termite workers defecate so violently that
they eviscerate or their guts literally explode, spewing out noxious materials onto their enemies. This
phenomenon is called dehiscence, and some termites have especially enlarged abdomens, full of
nasty chemicals, ready to dehisce. The termite, of course, dies some time afterwards. Autothysis is a
similar strategy, but in this case frontal glands in the head or thorax are enlarged and erupt explosively,
releasing noxious chemicals in a similar way. These workers are rather like suicide bombers!
To understand ant tactics, one must know what their goals are. Simply the goal of an ant nest is to
maximise the resources it exploits, so as to maximise the number of winged males and females that it
can release each year, as a few of the virgin queens must establish new nests if the ant race is to
continue. There are many species of ant and many races within each species all competing to ensure
their survival. The typical ant solution to the survival problem is fierce competition between nests and
cooperation between nest mates. Again this boils down to kin selection. Some ants are somewhat more
peaceful - exploiting what resources they find and only showing aggression when attacked. Others are
utterly and relentlessly aggressive.
Intelligence gathering. Ants employ both scouts and look-outs. The scouts not only search for new food
sources, but also report back any enemies that they sight. Sometimes the same scout will then lead a
battle party to engage the enemy, other times it recruits nest-mates who make their own way to the
enemy by following a chemical trail that the scout deposits on its return run. It is also important to
destroy enemy scouts before they can report back to base, and many ants go through considerable
lengths to react rapidly and overwhelm enemy scouts.
One effective strategy is to suppress enemy foragers - stop your opponents foraging and you stop
them exploiting resources that you can use instead. In the Arizona desert, the honeypot ant
Myrmecocystus mexicanus competes with the smaller red ant species Conomyrma bicolor. The
Conomyrma might well lose open field battles against the much larger Mrymecocystus, but the
Conomyrma rapidly locate the nest entrance holes of the Mrymecocystus, and while their own workers
forage for food, others deploy chemical weapons and drop small stones, which they carry in their
mandibles, down the entrance holes, on top of the enemy ants as they try to leave their nest. In this way
the smaller ants keep as many of the honeypot ants trapped inside their nest, reducing the number of
foragers they can field, leaving more food for the Conomryma ants. Note that this tactic of nest-blocking
is also an example of tool use.
Sappers. Ant nests are well-protected structures and like mediaeval knights sieging castles, some ants
employ sappers. The European thief ant Solenopsis fugax excavates tunnels toward the target nest. As
soon as one tunnel breaks through, the excavator runs back and recruits its nest mates who pour
through, spraying chemicals to repel the defenders and then steel the young brood and carry them
back for later consumption.
Kamikaze. Autothysis is known to occur in a Camponotus species of ant.
Slave-masters and thieves. A number of ant species steal food from enemy worker ants, intercepting
them, spraying them with chemicals to disable and confuse, then stealing their booty. This not only
suppresses the rival colonies, but removes the need to locate food. The robbers simply wait along the
enemy foraging trails or around their nest entrances. These ants can snatch food from opponents ten
times their size, and if counter-attacked, they use their small size to dodge and then run away, only to
return moments later. This phenomenon of food-stealing is called kleptobiosis. Often the thief ants
inspect the cargo of the target ants, and let them pass if they carry items they do not consider as food,
like bits of debris or vegetation, but rob them if it is an appropriate food item, like another insect.
Sometimes these thief ants will attack in mobs, sometimes individually.
Slave-maker ants raid the nests of other species and steal pupae from enemy colonies and rear them
to be their slaves. However, these ants are not slaves in the oppressed sense, since they grow up
believing their captors to be their own nest mates. Often the captors are so well armed that they are
unable to feed themselves and so rely on their slaves to feed and groom them. Some slave-makers use
several ant species a slaves, exploiting the characteristics of each. Peaceful species may stay home to
tend the brood, whilst aggressive species may accompany the slave-masters on their raids and help in
the fight. These ants may spray propaganda substances on the defenders, during a raid, chemicals
that confuse the enemy, causing them to panic and route. Some defenders inevitably stay to fight,
however, but the slave-masters are formidable combatants. Once they overcome resistance, they rush
into the brood chambers, steal the young and then rush out again.
Some ants will take prisoners from rival nests of the same species. For example, when one honeypot
nest over-runs another smaller nest, they kill most of their opponents, but spare the storage ants that
give these ants their names. These are individuals with massively swollen abdomens that store honey.
So swollen these ants are that they are not capable of combat and as valuable food stores they are
taken back to the victorious nest. The queen is killed and these honeypots have lost their ability to
perpetuate their own genes, but they are not mistreated by their captors, instead they are treated
exactly like fellow nest mates.
City defence. Nasutitermes nest in trees, keeping the nest out of reach of many predators. They
descend to forage amongst leaf-litter through covered galleries that they construct as a defence
against ants. Some termites and wasps will associate their nests with those of Azteca ants in trees.
Some social wasps even build their nests inside the nests of Azteca ants. Either the Aztec ants do not
consider these guests competition, or the guests somehow fool their hosts into accepting them. Many
beetles associate with ants and termites by deceit, we shall look at these guests of the ants later.
Several ant species associate with specific species of tree. The tree provides sheltered nests, often in
special structures, for the ants and may provide them with food from special nectaries. In return the tree
gains protection against herbivores - even large animals have to be careful about eating leaves from
such a tree.
Building nests underground or in hollow trees also offers them protection, from both extremes of climate
and from potential enemies. Some wasps build a nest suspended from a single stalk, which may be
coated in ant repellent and guarded by sentries. The stalk, or petiole, may also be smooth and slippery
to make it hard for ants and other insects to climb. If a nest can be reached and attacked, then strong
walls can certainly slow down even the strongest attacker, buying valuable time to rescue brood and
mount active defenses. The walls of the nest of the termite Macrotermes subhyalinus may be several
feet thick! It takes quite a large anteater to breach such walls.
Phragmosis is used by some termites and ants to either block the nest entrance or to block key
passages inside, such as those leading to the royal chamber.
Coordinated counter-attacks are a vital strategy employed by social insects. Species of stingless bees
can repel large attackers by biting ears, nostrils and eye corners. They also maximise the use of their
jaws on winged insect attackers by biting at the wing bases.
If all else fails, then it may pay to evacuate a nest. When Pheidole ants attack fire ant scouts and
destroy them, they will search for hours nearby to make sure no scout survives to report to base.
Sometimes, however, one slips through and then the fire ants arrive in greater and greater numbers.
The Pheidole ants are usually heavily outnumbered and despite being large and formidable fighters the
Pheidole soldiers face a losing battle. The Pheidole pull back toward their nest. The soldiers close the
defensive perimeter around their nest, making it smaller and smaller as they lose numbers. From this
perimeter some soldiers charge forth in counter attack. All the while the workers have withdrawn
completely and are busy evacuating the nest, taking the brood (eggs, larvae and pupae) with them.
This is a frantic evacuation and even the queen has to fend fer herself and make her own escape. The
soldiers buy as much time as they can and fight to the last. The Pheidole workers, now soldierless, will
wait until the fire ants leave their nest and then return. Their nest remains vulnerable until they rear up
a new crop of soldiers in a month or two.
Nation building. In many ant species, each nest possesses a single queen. Often, however, in the early
stages of nest formation several queens may pool resources to quickly establish a sizeable colony in
the face of stiff competition from other nests. This allows them to rapidly achieve a high number of
workers. However, there comes a time when the nest needs a single sovereign. Depending on the
species, the workers may select their favourite queen and execute the rest, or the queens may fight to
the death, sometimes assisted by groups of workers who take the side of one queen or another. Usually
when the single queen dies, she is not replaced and the nest slowly dwindles away. Other species
continue to have multiple queens in a nest, allowing the nest to continue if one or more queens die.
This also gives the nest tremendous reproductive power and such nests achieve 'supercolony' status,
such as a supercolony of Formica ants found in Japan, which covered 675 acres, possessed some one
million queens and 306 million workers!
Above: a formican ant fires formic (methanoic) acid from its modified tail sting (acidopore) at an attacker,
perhaps a large anteater above it. (Originally this Pov-Ray model used a cone containing scattering media to
simulate the spray (inset), but the more recent version uses more realistic bubble-like droplets).
Several studies have analysed the work efficiency of ants. One might expect that ants work tirelessly
in total devotion to the economy of their nest. However, the efficiency of ant labour, defined as the
amount excavated by a single worker, decreases as the nest size increases. This is not surprising,
when only half a dozen ants are available there is much work to be done, but once a nest becomes
established the ants spend more of their time resting. Ants do not waste their energies. Furthermore,
in any given colony at any given period of time, there are some ants who work much harder than the
rest, these are the so-called 'elites'. The number of elites generally declines as nest size increases.
Studies on work efficiency have also been conducted on dulotic ants. Dulotic ants exhibit the
phenomenon of dulosis - enslavement of other ants. This may happen when an invading queen kills
and replaces the queen of the host species, or the slave-makers may steal pupae from ants of other
species and rear them as their own. The slaves are not forced and no additional aggression is shown
towards them, rather the slaves consider themselves to be of the same kind as their masters. Thus,
slave-making species are parasitic on other ant species; to be specific they are labour parasites.
Some slave-making ants are simply lazy, their workers will do some work, but not as much as the
slaves. Others are totally dependent on their slaves and can do no useful work without them. For
example, Formica sanguinea and Polyergus samurai are both parasitic on Formica fusca. Formica
sanguinea will excavate at less than half the rate of Formica fusca when alone, whilst Polyergus
samurai will do no useful excavation at all. The presence of Polyergus in a mixed nest has no effect on
the work rate of the Formica fusca ants: they simply carry on working at their normal rate. Formica
sanguinea has fewer elites than fusca and the number of these elites drops more rapidly as nest size
Although this text is based upon a number of sources, one of the best and most accessible is the
outstandingly beautiful book by Holldobler and Wilson: Journey to the Ants, A story of scientific
exploration, by Belknap Harvard Press, ISBN 0-674-48525-2. This book is a must for all ant lovers!
Sakagami, S.F., and K. Hayashida, 1962. Work efficiency in heterospecific ant groups composed of
hosts and their labour parasites. Animal behaviour 10: 96-104.
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