Termites

Northern Australia is a big country shaped by a small insect: the termite. In many places the very look of northern savannas owes much to the mounds built by colonies of this insect. North Australian savannas have one of the most diverse range of termite mounds in the world: from the enormous buttressed “cathedrals” of spinifex termites, to the remarkably aligned “magnetic” mounds and miniature cities of columns built by various Amitermes species.

Mastotermes darwiniensis - one of many termite species that have nests largely hidden from view underground or in trees.

Even more termite species — around three-quarters of those found in north Australia — are hidden from view, building nests within trees or underground.

As far as we can tell, most of these termite species are only found in Australia.

Despite being surrounded by termites our understanding of the ecology of the different termite species remains limited. Although many of us are warily familiar with a few timber-eating pest species, most of the termite species of northern Australia, which may feed on grass, wood or humus, are largely unstudied. However, we can provide some answers to a few key questions.

Are termites the same as ants?

Termites are only distantly related to ants. Like the ants, bees and wasps termites are social insects that live together in well-organised colonies, however, unlike the other social insects which are all closely related, termites have evolved from cockroach-like ancestors and have independently evolved the social way of living. Like the ants, the termite colony is made up of different types of insects or “castes”: worker termites, soldier termites and reproductive termites with wings.

Close-up the worker termites, which comprise the majority of termites in most colonies, generally look quite different from ants — they have pale, soft bodies and are blind.

Termite workers (on the right) are usually a few mm long. Ants are a diverse group of insects and some species have very large workers such as this one from the genus Odontomachus on the left.

These broad differences can be traced back to their distinct ancestries. Ants, bees and wasps all undergo a dramatic change as they grow, transforming from grub-like larvae into fully developed adults via a pupal stage. Termites, like cockroaches, instead grow gradually from juveniles, which look like small mature insects, through a series of moults into progressively more developed forms — either workers, soldiers or reproductives.

Are termites the same as cockroaches?

Recent research on the genetics of termites has suggested that termites are so closely related to cockroaches that we should consider them as an unusually specialized type of cockroach – or in taxonomic terms they are more like a family within the larger cockroach order (Blattodea) rather than an order in their own right (Isoptera) (reference 1). However, whatever new insights are gained into their relationship with other insects, we can still happily distinguish termites from “other” cockroaches as the common names are unlikely to change.

Of ‘white ants’ and ‘anthills’

Termites in Australia are often referred to as ‘white ants’. Of course they are not ants (see above) but this term presumably came from the termites’ resemblance to ants – like ants they are encountered as wingless insects in groups but unlike ants, worker termites are often pale or even white – hence the term ‘white ants’.

There is presumably a similar origin in the term ‘anthill’ for a termite mound. The association of termite mounds with ants would have been helped by the fact that ant colonies often invade termite mounds and many termite mounds will have ants living inside some parts.  In most cases if you see ants living in a mound in northern Australia, it will be a termite mound. Relatively few Australian ant species build above ground mounds and they usually look quite different from termite mounds.

What do the different types of termites in a colony do?

If you could look inside a typical termite colony you would probably see that most termites were rather similar with small, pale bodies and no wings — these are the "worker" termites that make up the bulk of the colony. Looking a bit longer might then reveal a smaller group of termites with unusually shaped heads with large jaws, or perhaps with heads drawn out into long snouts for squirting chemicals — these are the colony's "soldier" termites. Depending on the time of year, further examination might then reveal termites with wings, either in buds or fully developed. These are the reproductive termites, or winged "alates". These different groups of termites are often called termite castes.

The reproductive termites develop in the way many other insects do: they grow wings, fully developed eyes, reproductive organs and a stiff, brownish skin. It is these alates which fly out from the termite colony each year to look for a mate. If they are lucky they and their mate will establish a colony and become the Queen and King termites of the new colony. The great majority of alates, however, does not survive the mating flight.

Winged termites or 'Alates' - are generally poor fliers and few will survive a mating flight to become a Queen or King termite (below)

A Queen termite (left) with an enlarged abodomen for egg production and a King termite (right).

Most termites in the colony, however, never grow wings and never become sexually mature but have an inhibited, skewed development in which they acquire either strong jaws for foraging and mound building as the worker caste (or worker-like caste in some groups) — or acquire pincers or chemical weapons for defending the colony as the soldier caste.

Different termite species can have their own distinctive soldiers ranging from those with chemical defences (at left) to those with different shaped jaws (at right).

Neither of these castes develops compound eyes, sexual organs or fully pigmented skin and as result most residents of a termite colony are blind, thin-skinned and susceptible to dehydration — relative weaklings in the largely armoured and mobile insect Class. For more information see Termite Colonies

Why do termites live in colonies?

It is thought that the social organization seen in these insects offers a number of advantages — a key one being that a group of insects working together can achieve feats that enhance their survival that would be impossible for an individual insect. The obvious example for termites is their remarkable ability to cooperatively build well-insulated, often complex nests — and networks of foraging tunnels that spread out from the nest to food sources.

 

The large mounds constructed by magnetic termites Amitermes meridionalis (at left in background) and spinifex termites Nasutitermes triodiae (at right in foreground).

How long do termite colonies live?

We do know that the worker and soldier termites only live for a few years, but as the members of a colony are being continually renewed by new eggs from the queen, a colony can outlast individual workers and soldiers. So can we age the termite mounds to get an idea of how long the colony lasts? Unfortunately, unlike corals or trees, termite mounds cannot be easily dated by looking at growth rings. This is because in many colonies the termites are continually re-working the inside of the mound. Individual mounds have been observed to survive for decades.

 Insect Methuselah?

The history of one cathedral mound provides interesting clues as to the age of termites. When the Overland Telegraph line was being constructed, the top of this presumably tall mound was removed in 1872 because it interfered with the wires. At that stage it must have been already several decades old and, fifty years later, in 1935 it was still thriving. This colony may therefore have reached an age of almost 100 years, before it fell into disuse, sometime before the next inspection in the 1950s. Colonies belonging to this type of termite the spinifex termite (Nasutitermes triodiae) are believed to be derived from just one irreplaceable queen, the mound lasting just as long as she does, in which case she would be a very long-lived insect. However, we still know very little about the biology of this species and it could be that replacement queens are produced in these long-lasting colonies.

Researchers studying golden shouldered parrots reckon that that conical mounds used by the birds must be 30 years old or more before they are suitable for nest sites. They calculated a growth rate of between one and two centimetres a year for these mounds, some even decreasing in size.

How do termites establish new colonies?

The analogy of termite colonies with plants is also apt when it comes to dispersal, as like many plants they reproduce by allowing “seeds” to be dispersed — in this case the seeds are the winged male and female alates which fly out from the nests in coordinated swarms and then meet up after landing to try and reproduce and found new colonies.

A termite colony will usually take a few months to produce alates from larvae and in the tropical savannas, swarms of male and female alates are often released from nests at the onset of the wet season when the moist conditions are often suitable for starting a new colony. Alates are generally poor fliers and do not travel very far  —  understandable given that male and female alates need to meet up and dispersal flights of more than a few hundred metres reduce the likelihood of this happening. It may also disadvantage a colony with significant genetic investment in adaptations to a local environment to have long dispersal flights that risk leaving that environment. For more information see Termite Colonies

 All about mounds

You can see hundreds of the mounds built by termite colonies in some parts of the tropical savannas and it is easy to overlook the amazing feat of cooperation they represent. For example, consider a mature cathedral mound around 5m tall. Given it was built by insects around 5mm long this is equivalent to humans getting together and building a massive skyscraper over a kilometer high and covering many city blocks.  

Why do small animals appear to have super powers?

Termites can build towers a thousand times their own height, ants can lift objects many times their own size – are these “super” animals which through sheer luck happen to be too small to threaten us? Not really – much of their apparent "super" power stems from the very fact that they are so small compared to us. As animals get larger their muscles get more powerful but this occurs at a different rate to the way the objects those muscles need to lift get heavier as they get larger.

If you double the length or width of a muscle then, very roughly, the strength increases in proportion to the cross-sectional area of the muscle, so a muscle twice as wide and long could become four times as strong. But if you double the linear dimensions of an object that muscle might lift, that object becomes eight times as heavy, because you increase the volume by a factor of eight in doubling the width, depth and height.

So a flea can jump hundreds of times its own height, but if it was a hundred times larger - the size of a frog - its muscles might be around 10,000 times stronger, but its body would be a million times heavier .

For more information visit this part of the Flying Turtle Science and Technology site. 

Having mounds means these insects can survive harsh, dry conditions in the humid micro-climates of their nests, a luxury afforded to few other animals - a factor that may contribute to termites’ remarkable abundance in the seasonally-dry tropics (see below).

But there are limits to what a termite colony can accomplish. It appears it is more difficult to sustain suitable microclimates in above-ground mounds in the dry and cool temperate regions and consequently mound-building termite species are not particularly diverse outside the tropics. However, those species that live in hardier nests hollowed out in wood or under a protective layer of soil can live in the warmer temperate regions of Australia as well as the tropics.  

How many different types of termites are there?

There are more than 2800 termite species in the world. This is not many compared to the more than 11,000 different species of ants, but quite a lot compared to the 280 or so different marsupials. There are about 263 termite species found in Australia and around 160 of these can be found in northern Australia (reference 2).

Although termites all look pretty similar to our eyes, and although they are not as diverse as the ants, there is a marked difference between many of the species. For example, one of the smallest Australian species, Occultitermes occultus, has soldiers a little over 2mm long — compare this to Neotermes insularis soldiers with giant heads 7mm long and 15mm in length overall with large mandibles.

How abundant are termites?

While termites have a restricted distribution compared to the other social insects (ants, bees and wasps are found throughout tropical and temperate regions), what they lack in range they make up for in numbers. Termites can be extremely abundant in the tropical savannas and along with ants are the most abundant insects found in savanna soils . Savanna habitat covered in the large nests of spinifex termites, Nasutitermes triodiae, may support a few hundred tonnes of termite per square kilometer – far greater than the weight of cattle supported per square kilometre on similar soils.

What do termites eat?

This abundance is no doubt partly due to the fact that termites consume a widely available resource most other animals cannot exploit: the cellulose and lignin that stiffen the woody parts of plants. By virtue of symbiotic bacteria or protozoa in their gut, termites can digest the cellulose and lignin present in a wide range of wood and grass, living or dead, as well as the plant material in litter and soil – with individual species specializing on particular sources of cellulose.

For example over 80% of older eucalypt species were found to have been piped by termites (most likely mostly Coptotermes acinaciformis) in the woodlands in Kakadu National Park and those of the Darwin area (references 3 and 4).

 

A log piped by termites.

Termites and Didjeridus

The Aboriginal wind instrument, the didjeridu, is made from termite-hollowed trunks or branches of trees. In north-east Arnhem Land, for example, the common eucalypt species E. tetrodonta and E. miniata are used by the Yolgnu. While the termites do the work of hollowing out the wood, considerable skill and experience is required to select the tree and then prepare the harvested wood to make a good didjeridu (reference 5). Commonly it is the trunks of smaller trees that are selected and recent research (reference 4) has suggested that because smaller trees with very hollowed trunks are not likely to live very long anyway, traditional harvesting of trees for didgeridus does not have a great impact on tree populations. The same cannot be said for non-traditional modern harvesting where often larger trees are cut down and the branches harvested. The scale of non-traditional harvesting is significant and the impact on tree populations has yet to be quantified (reference 6).

Other species, such as the spinifex termites mentioned above, specialize on grass and many of the abundant termite mounds in the savannas are insect-crafted silos of chopped grass. There are also groups that specialize on the plant material in soil and humus, and groups that feed on the litter layer.

A mound of a nasute termite colony cut open to reveal the stored chopped grass

 Where do you find the different sorts of termites?

The termites that build mounds are concentrated in Australia’s tropical savannas while many tree- and soil-dwelling species are found in both tropical and warm temperate regions. It is likely that it is harder for termites to maintain a warm, humid environment in an above-ground mound – which may also need to have good ventilation for storing the grass the termites eat – than it is for termites to maintain stable conditions inside wood or under soil.

Relatively few species of termite are found in Australian tropical rainforests or monsoon forest patches (reference 7). This appears to have little to do with the rainforest environment itself as similar habitats in South East Asia and South America can have very high termite diversities. It may be a legacy of the fact that when rainforests were initially established in Australia few rainforest-adapted termites came with them.

 Why are there different types of mounds and nests?

Given that their nests and mounds appear to provide stable internal conditions for termites in a wide range of environments it is perhaps not surprising that many nests appear to be shaped to suit those different environments. This is seen in Amitermes laurenis: in well-drained habitats it builds small dome-shaped mounds, yet in seasonally flooded flats it constructs huge mounds aligned along a north-south axis, often hundreds of times larger. Studies on this species and A. meridionalis, which also builds oriented mounds, suggest that such mounds are an adaptation to the seasonally waterlogged conditions: the high surface-area shape oriented north-south creates a stable environment for living above the ground in flooded habitats where migrating to an underground refuge is impossible. Recent genetic studies imply this behaviour may have evolved several times and more than once within A. laurensis (references 8 and 9).

 

'Magnetic' termite mounds built by Amitermes meridionalis appear to be adapted to seasonally flooded habitats

Other savanna mound-builders such as the spinifex termite N. triodiae also show great variation in mound type which may also be related to local environmental conditions: mounds with higher surface areas, which may facilitate better ventilation of stored grass, being found in the northern, more humid locations. However, this relationship has not been studied yet.

Two types of mound bult by Nasutitermes triodiae - the tall, fluted "athedral" type found on the Top End of the NT and the smaller, bulbous mound found further south in the Kimberley region.

There is no reason why we should not expect the nests built within wood and under the soils to have a structure and shape that is also adapted to local environmental conditions. In this way termite colonies and their nests may be rather like plants, which are also stuck in one spot, that have trunks, foliage and root systems adapted to suit local conditions. For more information see Variety of termite mounds

What impact do termites have on other plants and animals?

Termites can occur in great numbers with millions of them in a single colony and they also release their flying reproductives in simultaneous flights from many colonies, so the result is often thick swarms of alates that are a food bonanza for local animals like ants, small mammals, birds, spiders, frogs and lizards.

These swarms are effectively a large aerial injection of nutrients into the ecosytem – nutrients that have been liberated from the cellulose in dead wood and grass.  This dead wood and grass is abundant in the dry season and were it not for termites, many of the nutrients locked up in this plant material would be dispersed by burning. Termite nests also house these nutrients in the bodies of the termites and in the salivary and fecal material in their walls and when the nests eventually decompose they allow  those precious nutrients to re-enter the soil to be available for plant growth.

Termite colonies are one of the few living things that can sustain this cycling process through the northern dry season. While other decomposing organisms like bacteria and fungi struggle in very dry environments, termites function with year-round life-support from the humid nest. Not only can they maintain their nutrient cycling, but through their underground activity they also assist water penetration in soils. Such insect-driven nutrient cycling may be more important in Australia than it is in other tropical savannas like those of Africa, where large herbivores are significant in nutrient cycling (reference 10). For more information see Animals that Nest in Termite Mounds and Termite Predators

Termites and People

Despite their important role in ecosystems, termites have unfortunately become victims of what marketers call the Bad Apple Syndrome: the handful of species that attack buildings and agriculture have sullied the reputation of that great termite majority that pose no such threat. That early European settlers had a more jaundiced view is hardly surprising: reports tell of Mastotermes darwiniensis completely destroying a homestead and its fences in 2-3 months (reference 11).

Indigenous people of the tropical savannas, however, have long recognized termites as useful: for medicines, for dietary supplements, their carton for cooking, and mounds for camp fires. Recently however, their profile in the general community has changed in the north with large termite mounds now seen as tourist draw cards and being featured in nature documentaries. Termites are also being investigated as a possible indicator species for monitoring soil condition.

Conservation Issues

Should we go a step further and be concerned about threats to termites? Termites are not immune to global changes in the environment and there is evidence, for example, that vegetation thickening in Cape York Peninsula and the Northern Territory may be having an adverse impact on populations of “magnetic” mound-building Amitermes colonies. Dead and dying nests of these slow-dispersing insect colonies that build mounds oriented to the sun, have been observed apparently trapped beneath a slowly increasing shade from canopy cover. However even for these relatively well-known species we simply don’t know enough about their ecology yet to make definitive assessments of their conservation status.

References cited

(1) Inward, D., Beccaloni, G. and Eggleton, P. (2007) Death of an order: a comprehensive molecular phylogenetic study confirms that termites are eusocial cockroaches. Biology Letters Vol 3 (3) pp. 331-335

(2) Smith, G.B., Roach, A.M.E., Rentz, D.C.F., Miller, L.R., Abbey, H.M., Watson, J.A.L., Balderson, J., Cassis, G. and New, T.R. (1998) Zoological Catalogue of Australia Volume 23 Archaeognatha, Thysanura, Blattodea, Isoptera, Mantodea, Dermaptera, Phasmatodea, Embioptera, Zoraptera. CSIRO/ABRS Australia.

(3) Fox, R. E. and Clark, N. B. (1972)  The incidence of termites in eucalypts of the Darwin area.  Australian Forestry Research 5, 29–36.

(4) Prior, L. and Werner, P. (in press) Tree-piping termites negatively correlated with growth and survival of host trees in savanna woodland of north Australia Journal of Tropical Ecology

(5) Taylor R., Cloake J, and Forner J. (2002)  Harvesting rates of a Yolgnu harvester and comparison of selection of didjeridu by the Yolngu and Jawoyn.  In Harvesting of didjeridu by Aboriginal people and their participation in the industry in the Northern Territory (ed. R. Taylor) pp. 25–31.  Report to AFFA Australia.  Northern Territory Parks and Wildlife Service, Department of Infrastructure, Planning and Environment, Palmerston, NT.

(6) Forner J. (2006)  The globalization of the didjeridu and the implications for small scale community based producers in remote northern Australia.  International Journal of Environmental, Cultural, Economic and Social Sustainability 2, 137 – 148.  www.sustainability-journal.com.

(7) Dawes-Gromadzki, T.Z. (2005) The termite (Isoptera) fauna of a monsoonal rainforest near Darwin,northern Australia Australian Journal of Entomology 44, 152–157

(8) Jacklyn, P.M. (1992) ''Magnetic'' termite mound surfaces are oriented to suit wind and shade conditions. Oecologia 91, 385-395.

(9) Ozeki, M., Isagi, Y.,  Tsubota, H., Jacklyn, P. and Bowman, D.J.M.S.(2007) Phylogeography of Australian termite, Amitermes laurensis (Isoptera, Termitidae), with special reference to the variety of mound shapes. Molecular Phylogenetics and Evolution 42, pp. 236-247

(10) Andersen, A.N. and Lonsdale, W.M. (1990) Herbivory by Insects in Australian Tropical Savannas: A Review. Journal of Biogeography, Vol. 17, No. 4/5, Savanna Ecology and Management: Australian Perspectives and Intercontinental Comparisons (Jul. - Sep., 1990), pp. 433-444

(11) Gay, F. J., and Calaby, J . M. (1970) Termites of the Australian Region. In Biology of Termites. (Eds K. Krishna and F. M. Weesner.) Vol. 2, pp. 393-448. Academic Press: New York and London.