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CSIRO Feature Article:
Trouble with Termite

By Roger Beckmann


When you think of architects and builders, you expect them to be human, don't you? Well, think again . . . there are large, highly organised structures on Earth that weren't built by humans. There are even plenty of them right here in Australia. They can be more than three times the height of a person, and some even have covered walkways radiating out from them. So where are these things, and how did they get there? The answer is that they're the work of tiny termites, responsible for building the skyscrapers of the insect world.

But that's not all these little insects can do. It's no difficulty for them to fell large trees, chew up electric cables and demolish houses! Considering most of us rarely see them, termites are pretty important - in fact, despite their small size, they're some of the most important living things in many of our tropical and arid ecosystems. But at the same time they're one of the most feared of all insect pests.

Castes of thousands

Termites are called social insects because they live in complicated societies with thousands or even millions of individuals working together for the benefit of the colony. Each termite species forms its own colonies, and within a colony there are several forms of termites. These forms are called castes, and different castes have different functions.

The four castes of termites (clockwise from top left): queen, king, worker and soldier.


Ants, bees and wasps also live in colonies with castes. Most people would know that the most important individual in all these colonies is the queen. The same is true of termites, though at the start there's also a king. The future king and queen termite have wings when they're born and are sometimes called the reproductive caste. They emerge from mounds and fly around to find a mate. This is known as the colonising flight - but it's more like a death flight because very few termites survive the flight to go on and produce a colony. After they have paired up, the termites shed their wings. Each pair will then try to set up home in a suitable spot - somewhere moist and protected, such as a piece of decaying wood on the ground. They hollow out a small, cosy space in which they mate and shortly thereafter the female lays her first batch of eggs. When these hatch, the king and queen are the ideal parents, carefully feeding and caring for their offspring.

The Queen Mum

The first young grow up to become the workers of the colony, and a new society begins. The queen lays more and more eggs. However, it takes quite a while (up to a few years, depending on the species) for the colony to have enough termites to be noticeable. At first the queen helps with various tasks, but as the number of workers increases they feed her and also tend all the young. The queen is the mother of all the other termites in the colony apart from the king. She lives (sometimes for up to 50 years) while hundreds of generations of her workers and personal attendants die and are replaced.

The queen is fertilised from time to time by the smaller king. He is long-lived compared to the workers, but doesn't usually last as long as the queen. Extra 'kings' may take his place when the colony is large enough to begin producing reproductives. If so, these kings will stay in the colony and mate with their own mother!

If the queen dies the colony can still continue. Supplementary queens from the reproductive caste may take over as egg-layers. They're not usually as large or productive as the primary queen, but several of them may work together to replenish the population.

Workers and Soldiers

The real hard slog of making a termite mound falls to the workers. Usually the great majority of termites belongs to this caste. Every day some leave the colony to gather food, while others build and repair any damage or feed the young or the queen.

Soldiers may have powerful jaws with which they cut or stab intruders, or a long tube on their heads from which they squirt chemical weapons - sticky stuff to trap invaders or toxic chemicals to deter them. In some species the soldiers can squirt their toxic brew with great accuracy for a distance of several centimetres.

The soldiers' job is obviously to defend the colony against invaders, which usually means ants. When workers are repairing damage on the edge of the mound, soldiers are usually present to guard them, their heads facing outward to counter any threat. The soldiers, despite being prepared to sacrifice their own lives, often simply aren't powerful enough when they're pitted against large numbers of ferocious ants, larger insects or other animals. The main defence is really the enormous mound itself. This ensures that the core of the termite society is protected from almost every conceivable threat, even though individual termites will inevitably be crushed or eaten as they leave the mound or work on its edges.

Although most termite species in Australia don't build above-ground mounds - preferring instead to nest below ground or in wood - those that do tend to produce spectacular structures. If you've ever pulled a bit off the outside of a mound, the chances are that you'd have seen a few workers and perhaps soldiers. You wouldn't have seen the millions of busy workers or the real heart of the society, which lies deep inside the mound and partly underground. Some termite species even keep farms inside to help feed their society. They lay out wet, chewed up plant matter, inoculate it with fungus, and then harvest and eat the mould. Busy workers tend these gardens and take the food for others in the colony to eat.

The giant mounds of the Cathedral Termite (Nasutitermes triodae) are among the largest in the world.

A termite colony typically lasts for 10-20 years, but some are known to be 60 years old. The mounds are built to last! And if they are damaged - by heavy rain, flooding or fire, for example - the hard-working citizens quickly repair them!

Magnetic Mounds

Some of the oddest mounds are the so-called magnetic mounds in the Top End, which occur in groups, with each two-metre tall mound being the same shape and with all of them positioned accurately to face in the same direction. A collection of these mounds looks frighteningly alien at first sight. How could they all be aligned in the same way? And why?

Research suggests the alignment of the mounds is designed to help the termites avoid unfavourable temperatures. Usually, termites can withdraw into the inner galleries of a mound when conditions outside are too cold, wet, hot or dry, but the species that build the magnetic mounds live in areas that are flooded during the wet season. The ground is completely underwater for weeks, so the bottom of the mound is flooded. Temperature regulation within the above-ground portion is therefore very important. The eastern face of the mound then becomes the part of the colony that's kept at a reasonable temperature. In the early morning it's heated by the sun, but soon the sun moves and this face remains in the shade and at a reasonable temperature for the rest of the day, while the north-facing side takes the heat.

 

caption: Magnetic mounds are believed to be designed to help regulate temperature.
credit: Photo by David Curl

In areas where windy conditions mean the east faces of mounds take longer to warm, scientists have found the mounds may be positioned so the sun remains for longer on the eastern face. The mounds are not an exact and rigid compass, but vary in different places to benefit the termites. It seems very carefully calculated! The termites may be using the Earth's magnetic field to decide on the positioning of their mounds, but we don't yet know for sure.

Teeming with Termites

CSIRO scientists estimate that there are about 350 termite species in Australia. Most species occur in the hotter parts of the country, with more than 100 species occurring in the Top End of the Northern Territory. Scientists haven't even got around to naming most of these species, but they've established that the great majority of termites fall into one of four groups: wood-eaters, soil-eaters, debris-feeders (which eat plant litter and dung) and harvesters (which cut down living grasses and herbs). Only about half a dozen or so are serious pests. Wood-eaters are quite harmless if you find them - even the soldiers' jaws don't do much to us - but their craving for wood can ruin our furniture, houses or even bridges.

caption:

There are about 350 different species of termites in Australia.

A survey of hundreds of houses in New South Wales in the 1980s showed that about one in five houses had active wood-eating termites around or had had a problem with them in the past. The results of the termites' huge appetite for wood can be very dangerous, but often go unnoticed because the workers tend to shun light and dry air. They build covered tunnels or galleries from their nest and eat wooden structures from the inside - so roof timbers and doors may seem intact when in reality they're just a thin shell with nothing but dust and termites inside. Then, suddenly, they can collapse.

Termites eat wood from the inside out, so damage can go unnoticed until it's too late.

Scientists at CSIRO Forestry and Forest Products and CSIRO Building Research have studied the problem of termite damage in detail - and they've enlisted the help of Double Helix Club members.

Vital Cogs in the Ecosystem

Termites are much more than just fascinating insects that live in organised colonies. They are an essential part of many arid and tropical ecosystems - in particular, those in northern Australia.

Have you ever wondered why Africa has so many large mammals while tropical Australia - with a very similar climate - does not? Where are our elephants, giraffe, wildebeeste, rhinos and zebras - or their Aussie equivalents? The answer to this question is complex, but studies of termites have recently given us a better understanding of the nature of our own ecosystems.
Ecologists have suggested that the infertile soils and the very seasonal rainfall in much of northern Australia make it too hard for the place to sustain herds of large mammals. But the lack of the big mammals has given other creatures more of a look in. Reptiles and insects are the winners.

In the Top End of the Northern Territory, termites are present everywhere. They are decomposers and important consumers of plant material. As they munch their way through wood, leaf and stem they unlock the nutrients that the plants have accumulated and store them in their nests and in their own bodies. Termite nests are 'nutrient hotspots'. As old nests decay and erode, so vital stores of nutrients from decades ago are slowly released, ready to be used again. Without the activity of the termites, nutrient cycling - on which life depends - would be greatly reduced. This is especially true during the long, hot dry season. During this time plant growth slows and most plant-feeding insects become inactive, but termites are as busy as ever, feeding on dead and dry plant material instead.

In addition, the termites are a useful food source for other creatures. Ants, spiders and lizards are especially partial to a termite feast, which can be had at any time of the year. In this way, feeding chains are built up. Scientists have discovered that in areas of the Top End with plenty of termites there is more variety in the ant and reptile fauna.

Tonnes of termites

In many parts of tropical and sub-tropical Australia there are grassy grazing lands with a few trees remaining. Here farmers run cattle but, because of the dryness and poor nutritional quality of the grasses, one cow needs about 25 hectares to graze on. On average, the weight of cattle flesh (the 'biomass') works out at about 24 kg per ha. CSIRO scientists have surveyed the termite presence in these areas and have calculated that the weight of termites ranges from 40 kg to a staggering 120kg per hectare. That's a lot of termite flesh - and makes these little insects much more important as converters of plant material than the cattle.
Termites could be serious competitors with the cattle - but the good news is that the termite activity, by eventually putting nutrients back into the soil, takes the place of fungi and earthworms in wetter environments, so they have an important place in the ecosystem.

Canberra Double Helix member Paul Britton showing tree damage caused by termites.

So what are they?

Termites are sometimes called 'white ants', but they're not ants at all - in fact, they're not even closely related to ants. So what are they?

Entomologists have worked out that termites are really a type of specialised cockroach! But you won't find them scuttling under your fridge looking for food scraps. They diverged from cockroaches on the evolutionary tree many millions of years ago, and have successfully pursued their own plant-eating life ever since.

Termites are small (their size can range from about 3 to 10 mm long), pale or transparent, and have thin skins. Unlike ants they don't have a thin waist, they are usually blind (there isn't much need for vision in the dark tunnels they inhabit) and they cannot tolerate dry conditions. But they are similar to ants in that they occur in large numbers and look busy! Ants and termites also both have castes that include sterile workers and soldiers, and a single large queen. Both insects can live in large, complex colonies and both have produced fungus-cultivating species - one of the more amazing examples of convergent evolution, where two species begin from a different point and end up quite similar in the way they live.

Termite tidbits

  • termites are major pests in Africa, Asia and the Americas as well as Australia
  • there are about 12 000 trillion termites on Earth
  • the mass of termites is about 10 times greater than that of all the people in the world
  • termites are thought to be responsible for about 40 per cent of the global release of methane, a greenhouse gas
  • termites chomp their way through about 7 billion tonnes of plant material each year

(Statistics from RMIT Openline.)

 

Measuring the gases emitted by termites - they're thought to contribute about 40 per cent of the world's methane.

And one for all

Faced with complicated societies in which an individual will lay down its life for the good of the group - such as ants, bees, wasps and termites - biologists have asked how such behaviour has come to be. Giving up an advantage for the good of others, with no immediate reward in return, is called altruism. It's often highly valued in our own society, but why should it occur in insects? If an altruistic individual dies, why does anyone bother volunteering?

Part of the answer lies in the fact that most individuals in insect societies cannot reproduce. The only way for their genes to be passed on is to help the society as a whole, because the entire colony is composed of their siblings. If they protect the young and the queen (who's their mother), the workers and soldiers are ensuring that at least some of their own genes survive. In the same way, many animals that don't live in societies show parental behaviour - working hard or sacrificing themselves to protect their young in order that their genes will continue in the next generation.

Another way of looking at social insects' selfless behaviour is to view the entire colony as one creature. In this case, each individual termite is merely a cell. Just as a single cell in our body will die for the good of the entire body - for example, if you cut your skin or to fight infectious germs - so too will a termite. An individual termite is easily replaced. Hundreds of foraging termites are destroyed or lost every day but the colony survives, just as millions of our own cells die every day but are replaced with new ones. In this sense the entire colony is one animal, and the giant mound is just a shell that it makes for itself. The control of this 'creature' comes from the queen, because the chemical signals she releases control the behaviour of the other termites, just as nerves and hormones - many coming from the brain - control the cells in a body like ours.

The distinction between what is one animal and what is many is very hard to make. Your own body, for example, houses thousands of millions of other organisms in your intestines; as well as this, mammals such as us may well harbour ticks, fleas, lice and worms. Looked at this way, every animal is a sort of mini-zoo. Inside an individual termite's digestive system are millions of tiny microbes. They produce enzymes that can digest cellulose, the main chemical in termite foodstuffs. Without them a termite would die of starvation because its own body is unable to make the enzymes it needs.

Big and destructive Mastotermes darwiniensis - which, as its name suggests, was first noticed around Darwin - is one of the largest termites in the world. It is also incredibly destructive. As well as wood it can chew up electric cables, leather, wool or rubber. It can also eat many plants in your farmyard or garden! Trees don't stand a chance - Mastotermes enter them through the soil and, when they reach the inner bark, they create deep grooves right around the trunk, quickly ring-barking (and thus killing) the tree.

Termites can eat the floor right out from under your feet!

 

Medical mounds and musical mounds

If you're ever feeling crook when you're in an isolated part of the Top End, head for the nearest termite mound. Aboriginal people use soil from termite mounds as a medicine for various ailments. You can eat the soil (no-one said medicine's supposed to be nice), mix it up into a watery paste and eat it, drink it, or put it on your skin. Termite mound soil is used to cure diarrhoea and stomach pains, to prevent bleeding and to stop some infections.
Scientists haven't studied in detail why termite soil should be a medicine, but it could be that the clay in the soil acts to 'bind up' loose faeces (similar to the effects of kaolin, a clayey material that's used in western medicine). Termite mounds are also known to be rich in many nutrients and minerals.

Termites aren't just handy for medicines. Without them you couldn't make a decent didgeridoo. These beautiful musical instruments are always made from hollow branches. And who hollows them out? You guessed it: the hard-working little termites. They get into a tree and eat the wood on the inside. Perhaps it's bad news for the tree, but good news for lovers of that unique Australian sound.

While termites' ability to hollow wood out is bad for houses and trees, it helps produce didgeridoos.


This article is reproduced with permission from The Helix, CSIRO's Double Helix Club magazine
Phone: Simon Torok (02) 6276 6643, Email: education-programs@helix.csiro.au
Web: http://www.csiro.au/heli