Dr Theodore Evans, Associate Professor at the University of Western Australia in Perth, explores termite nest structure, location, development, mobility and foraging behaviour and how this impacts the choice of termite treatment.
Termites are social and build nests in which they live – sometimes for decades. This is unusual for insects. Most insects are solitary and do not build anything, let alone a complex nest that serves as a functional, multi-generational city. So termites are different, and understanding nests will help to understand termites.
Nests come in a variety of numbers, shapes and sizes, and may be located in different positions, all dependent on species. Some species have just one nest in their colony, whereas others may have more than one. Multiple nests may be similar in size, or one may dominate. They may be housed within a food source or separated from all food. Species with separate nests may have short or far foraging distances, with nests from a few to dozens of meters away from food.
Understanding the nesting pattern of a species may help in managing that species. Consider the difference between a species with one nest that is always close to food, compared with another species with multiple nests that can be far from food. The best choices for management will differ between these species. Once a management system is installed, continued observation of the termites in the property may give more information about the termite species and potential location of the nest/locations of the nests. This should help control the termite infestation faster and more completely.
What is a nest?
Termites create nests in which they live and reproduce. This means that nests house the members of the colony that reproduce (the queen and king) plus the output of reproduction, the eggs and young.
Termites may build a variety of structures (see Glossary box), but if they are not used for reproduction, meaning they lack reproductives and young, then they are not nests.
Nest type and position
The position of the nest is descriptive. Four common types of nests and their positions are:
- arboreal nests on branches of trees;
- mounds on the soil surface (called ‘epigeal’, meaning ‘on earth’ by scientists); mounds can be freestanding or attached to tree trunks or rocks;
- trunk nests built inside tree trunks; and
- subterranean nests built under the soil surface (called ‘hypogeal’ meaning ‘under earth’).
These definitions are somewhat arbitrary and can overlap. Definitions can change over the life of the termite colony. For example, a Coptotermes acinaciformis nest often begins in a tree trunk or a stump (trunk nest) and then it erupts out of the tree as the colony grows and the tree trunk is no longer wide enough to contain it (mound). Definitions can change over an environmental gradient, such as rainfall. For example Nasutitermes exitiosus, found across southern Australia. In the east, along the wet coast of NSW, they have enormous mounds – two metres high. Moving westwards, into the drier interior, mounds shrink and sink underground. So by the time you get to SA, nests are entirely subterranean. This change is about maintaining constant humidity in the nest.
Nest organisation and foraging behaviour
Termites build a wide array of nests, more diverse than any other insect group. At their simplest, nests are simple excavations in wood. As the wood is also the colony food source, these excavations may be little more than excavations made during feeding. The most complex nests are built from soil, with faeces and saliva used as glue, often inside larger constructions. These may have special areas. These are the ‘royal chambers’ for the queen and king, and the ‘nursery’ for the offspring. The nursery may be used by all termites when they grow, as they moult in the safety of the nest. Other structures around the nest can be used for food storage and/or defence.
One-piece nesters: dampwood and drywood termites
In general, the simplest nests are found in the more primitive or basal termites, like the Termopsidae or ‘dampwoods’ and Kalotermitidae or ‘drywoods’. These termites either only rarely tunnel in soil (Porotermes in the Termopsidae and Neotermes in the Kalotermitidae), or don’t tunnel in soil at all (Glyptotermes, Cryptotermes and most of the Kalotermitidae). These are called one-piece nesters as the termites live and nest within their single food resource, and as they don’t tunnel in soil, it is always one single food resource.
Their nests are the excavated hollows left in the wood after feeding. There are no special areas for reproductives or young, although these are often clustered in one area of connected chambers. As the termites eat and hollow out their food resource, they move into uneaten wood. Thus the nest (such as it is) moves over time. In natural habitats, the single food resource may be the dead branch stud on a tree, and the nest moves down the stub and into the tree trunk. In urban habitats, the single food resource is often a timber beam, but these termites can move between joined beams (e.g. frames and roof trusses).
Subterranean termites
Termites that tunnel in soil are generally called ‘subterranean termites’ in Australia; the capacity to tunnel in soil is what makes them ‘subterranean’. Tunnelling allows subterranean termites to find and move between more than one food resource. Tunnelling is essentially manipulating soil – moving it aside to make a space in the soil. It is a small step in manipulating soil for tunnelling to manipulating soil to build with it. Building with soil allows more complex nests. The more complex nests are usually found in more derived species. More complex nests arise from tunnels connecting more than one food resource and may mean more than one nest.
There are two general forms of nest organisation in subterranean termites: multi-site nesters and central site nesters.
Multi-site nesters
Multi-site nesters have two or more nests connected by tunnels through the soil. These are nests, and so contain reproductives and young. Food is collected and returned to each nest. Think of a network of tunnels with two or more nests scattered over the area. In general, multi-site nesters build their nests in food resources (e.g. dead wood on the ground, such as fallen branches, or stumps) and use these nests until they have eaten out the food resource. Once the food resource is exhausted, the nest is abandoned and a new nest is built in another, nearby food resource. Thus nests are usually temporary (although a large food resource may persist with a nest for several years). Examples of multi-site nester termites include Mastotermes in the tropics, and Schedorhinotermes and Heterotermes all over Australia.
Central site nesters
Central site nesters have a single central nest that contains the reproductives and the young. Food is collected on the periphery and returned back to the central nest. Think of the spokes of a wheel as the foraging tunnels with the central nest at the central hub. In general, central-site nesters start their nests in a food resource (e.g. dead wood on the ground) and eventually eat out the food resource, but because new food is collected and returned to the nest, the nest is enlarged and fortified. Thus nests are usually permanent. Examples of central site nester termites include Coptotermes, many Nasutitermes, and some mound-building Microcerotermes.
Most of the Rhinotermitidae are multi-site nesters, and many Termitidae are central site nesters. But this is not always the case. Coptotermes are in the Rhinotermitidae and are central site nesters, Nasutitermes and Microcerotermes are in the Termitidae and some species are multi-site nesters (especially in the tropics of Southeast Asia). There is variation in many groups of termites.
Central site nesting species generally have larger populations in their colonies than multi-site nesters. This is typically true when considering a single nest of a multi-site nester. However, the combined populations of all the nests in a large multi-site nesting colony can rival the population of a central site nester.
Foraging and nest development
Drywood and dampwood termites
The single site nesting dampwood and drywood termites typically stay contained inside the single piece of wood. A few species can venture beyond the single piece, and depending on the circumstances, even tunnel in soil. The best-known example of this is Porotermes, especially at higher elevations. Most subterranean termites are temperature-sensitive, with Nasutitermes most sensitive and Coptotermes next, thus these termites are rarely found at higher elevations, with correspondingly lower temperatures. With the reduced competition, Porotermes happily tunnel through soils for distances up to 10 or 15 metres, as observed in the Adelaide Hills, the Dandenongs and other taller elevations in the south of the country. This is also observed in Tasmania, where dampwood termites exist and subterranean termites are completely absent.
Subterranean termites
There are similarities and differences in foraging between multi-site nesters and central site nesters.
The similarity is that they both tunnel through soil extensively to find food resources, collect food from those multiple feeding sites, then return the collected food back to the nest/s.
The difference is that multi-site nesters have multiple nests, so generally the multi-site nesters are travelling shorter distances between any one food resource and the nearest nest. In comparison, central site nesters are travelling longer distances, as all food is returned to their single central nest.
Inside those nests there are differences in the queens. In multi-site nesters, there are multiple queens, and they are physogastric but only modestly so. This is relative to the amount of food brought back to each smaller nest. In central site nesters, the single queen attains a larger physogastric size. Again, this is relative to the greater quantity of food brought back to the single central nest.
Nest mobility
As has been discussed above, some termites move their nests. This is observed in species that nest in wood. As the wood in which the nest in located is consumed, the nest disappears. The colony is going to need a new home. As the wood-nest disappears, foragers will search for a new food resource of a certain minimum size to use as their new nest. Once they have found a suitable sized piece of wood, they will relocate the queen, king and young to that new piece of wood.
The amount of time a nest will persist depends on the size of the wood. Smaller pieces of wood will persist a short time, larger pieces a long time. For example, a ground-out tree stump, when only the major roots are left in the soil, might last for months, maybe a year or two in the south. In comparison, a tree stump (no grinding) might persist for a few years, and a standing dead tree may persist for decades. In the tropical north, resources are consumed much faster.
Our best knowledge of relocation of nests actually comes from long-term studies of Mastotermes in Darwin. Mastotermes are very good at killing trees – they ring bark the cambium layer – and then they nest in the dead tree trunk, eventually hollow it out and move onto the next tree. When we brought mangoes to Australia (mango is native to India and Southeast Asia), Mastotermes discovered a new tree species that they really love to eat! They can wipe out whole plantations, moving like a wave through the plantation, relocating their reproductives from tree to tree as the trees are killed.
Some interesting points to note
Bivouacs
Bivouacs are superficially similar to a nest but they serve a different purpose. They are built from partly and even fully digested wood, depending on the termite species. They are found in species that have very long foraging distances and are used as a staging post and for resting and food storage. Food is moved into and stored in the bivouacs, partly for consumption and partly for later transfer back to the central nest. They are not used for reproduction and so do not contain eggs or reproductives. However, there may be numerous young nymphs in the bivouac – young nymphs will forage with workers, returning to the central nest to develop into reproductives as they get older. If the bivouac gets isolated from the central nest through movement, physical disconnection or even the result of a termite treatment (e.g. treated zone around a property), then it has the potential to become a secondary nest. (If a pest manager finds such as structure in a building and it does contain reproductives then it is the actual nest!)
Schedorhinotermes
Large soldiers and larger workers are female, small soldiers and smaller workers are male. Typically, the larger soldiers spend time close to the nest and near the queen. Therefore, when large soldiers are observed a building, the nest is likely to be nearby – the greater the number of large soldiers, the closer the nest. Conversely if only small soldiers are observed, it is likely that the nest is further away. As Schedorhinotermes are multi-site nesters, any building with these termites should be assumed to have more than one nest. Note that nests may be on neighbouring properties.
Heterotermes
Heterotermes tend to explore smaller food sources to avoid competition with Coptotermes and Schedorhinotermes. They produce all types of reproductives and are multi-site nesters, so ‘bud’ all the time. In addition, they generally don’t forage far from their nests. Therefore if Heterotermes are found in a building, it should be assumed there are multiple nests in the area.
Summary of Termite Genera Nesting Information
Nest type and termite treatments
Termite nest type, location, and nest organisation are factors to consider when designing a termite treatment. This is so if the aim is to protect a building, but it is particularly pertinent if the aim is to remedy an infestation inside a building.
A chemical barrier in soil around a house is a common treatment to protect the house from termite infestation. If the nest is outside the building, then the barrier should act to keep them there and protect the building. However, the chemical barrier works by stopping termites from crossing, whether they are inside or outside the barrier. So if the nest is inside the building, then a chemical barrier may act to contain (to ‘trap’) the termites inside the building.
If a chemical barrier is installed as part of a remedial treatment, and foraging termites become trapped inside the building, then nest organisation may be important. The greater challenge comes from multi-site nesters. First, these species may have built a nest inside the building, so the chemical barrier just separates the nests and so creates two colonies. Second, a nest may be built by the foraging termites trapped inside the building, as multi-site nesters usually have capacity to develop secondary or replacement reproductives. Nymphs may forage with workers and soldiers, and so nymphs may mature into nymphoid secondary reproductive (see glossary). Often workers can mature into ergatoid secondary reproductive too. Either way, a new nest can emerge, ‘budded’ away from the original nest due to the chemical barrier.
Central-site nesters are simpler. In most species, workers and soldiers are sterile, so foraging termites trapped inside a building will eventually die without any offspring. However, early stage nymphs may forage with workers and soldiers, and so these nymph may be trapped too. If this occurs, then nymphs may mature into nymphoid secondary reproductives, and so a new nest can emerge. This is less likely in central than multi-site nesters, as early stage nymphs are present for just a few months, generally in late summer, early autumn.
Baiting may be the preferred treatment if the aim is to remedy a termite infestation by colony elimination. By definition colony elimination occurs when all termites in the colony are dead. Baiting multi-site nesters, such as Schedorhinotermes, is more difficult than central site nesters. This is because multi-site nesters return the toxic bait to the closest nest, and the bait may not be distributed to other nests in the colony. Therefore the population of one nest may be eliminated, but not that of all the many nests in the entire colony. This explains the observation of termites reinfesting or ‘returning’ to a building some time after an apparent elimination. Eliminating each nest of the multi-site nesting colony make require more bait and much more time than a central site nester with a single nest. The time required may be reduced by placing more baits in more positions around a building infested with multi-site nesters.
Glossary
In discussing termite nesting behaviour, it is important to be clear on the various definitions…
Built structures: Termites may build a variety of structures for different purposes, depending on the species. The purpose may include reproduction, food storage, shelter and rest, and defence. A built structure may be used for more than purpose.
Nest: A nest is used for reproduction. At its simplest, a termite colony will occupy one nest, which contains the reproductives, eggs and larvae. A nest may exist without other structures, or (more commonly) may be enclosed within other built structures (especially those for food storage and defence). Some species may build more than one nest per colony. In these species, the first nest (initiated by the primary reproductives) is called the primary nest. Subsequent nests (sometimes initiated by secondary, supplementary reproductives) are called secondary or supplementary nests. Nests of more basal (i.e. primitive) species are usually built in wood and of wood-derived materials. Nests of more derived (i.e. advanced) species are usually built in soil and of soil.
Nest types: Arboreal nests are built on branches of trees. Mounds are nests built on top of the soil surface (also known as epigeal (‘on earth’) nests), and may be attached to trees.
Trunk nests are built inside tree trunks. Subterranean nests are built under the soil surface (also known as hypogeal (‘under earth’) nests). These nest types may overlap. Mounds may begin in (and erupt out of) trunks. Species may build mounds in wetter habitats and may build subterranean nests in drier habitats.
Nest organisation: In general terms, there are two forms of nest organisation. Central-site nests have one single central nest that contains the reproductives and young. Food is collected and returned to the central nest. Multi-site nests have multiple nests, each with reproductives and/or young. Food is collected and returned to each nest. Central-site nests are usually larger and contain more termites than any one multi-site nest, but all multi-site nests in a colony may rival central site nests.
Nest mobility: Some termites move their nests. This is observed in species that eat and nest in wood. Once the piece of wood, which is also the nest, has been consumed, the entire colony relocates to another piece of wood. The size of the piece of wood determines nest life (and colony size); fallen tree trunks may persist for years whereas fallen branches may persist for months.
Bivouac: A structure that is superficially similar to a nest, usually built from a matrix of chewed wood, sometimes with partially or fully digested wood, depending on the termite species. Bivouacs are often found in species that forage long distances away from their nests. They are used for rest and food storage, but not reproduction.
Reproductives: Termites that reproduce or are capable of reproducing; in other words males that produce sperm and females that produce eggs. A variety of reproductives are found among termite species, but no termite species make all forms of reproductives.
Primary reproductives: Termites that develop through the winged line, from egg to larvae to nymphs (with wing buds) to alates (with wings). They leave their natal nest, disperse and find a mate during the nuptial flight, and with that mate found a colony by themselves. Also known as imaginal reproductives (imago meaning the final adult moult in insects).
Secondary reproductives: All other reproductives. They may develop from the winged line: either alates that did not leave the natal nest (imaginal reproductives); or nymphs that mature early (i.e. without the imago, the final, winged alate form), which are also known as nymphoid reproductives. They may be from the wingless or worker line. In some termite species the wingless/worker is obligately sterile but in many it is facultatively sterile; in the latter wingless workers may develop into ergatoid reproductives. In a few dampwood/termopsid species the soldier may develop into a reproductive; the soldier-reproductive. If the primary reproductive dies, then the secondary reproductive is called a replacement reproductive. If the primary reproductive continues to live, then the secondary reproductive may be called a supplementary reproductive. Supplementary reproductives may live in the original nest, or in additional nests in multi-site nesting species.
Colony budding: For termite species with secondary nests and secondary, supplementary reproductives, the possibility of colony budding arises. This occurs when the secondary nest is separated from the primary nest, and so the secondary nest becomes independent. Termite species that have the capacity to bud can be moved by humans, when humans move infested wood or soil that contains reproductives, or termites capable of developing into reproductives. This is more common in multi-site nesting species, but is known of central site nesting species.
Flexibility: Note that many termites have flexibility in their development, nesting and foraging behaviours. Flexibility may be observed in unusual circumstances, such as new habitats. New habitats include non-native, invaded regions, or human-modified habitats, like urban areas. The information presented here is the typical or normal behaviour in most habitats. It does not preclude the occasional variation to other behaviours.
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