Termites

Termites are social insects that build large nests in soil or wood and can occasionally cause damage to wooden structures. They are sometimes called 'white ants', however they belong to a completely different insect group (Order Isoptera) to true ants (Order Hymenoptera).

Identification

Termites have pale brown to white bodies with a darker head and have no waist between the thorax and abdomen. The antennae have bead-like segments. The non-reproductive forms never develop wings, are blind, and have thin skin that makes them vulnerable to drying out. Reproductive forms have two pairs of equal-sized wings, one pair of compound eyes and a thicker skin that protects them better from drying out when exposed.

Habitat

Nests

Nests are formed either in trees, in soil mounds or underground. There are 5 main nest types and many species will build more than one type of nest:

• Ground mounds
• Tree nests (outside tree, connected to internal cavity)
• Pole nests (on human structures such as fence posts and telegraph poles)
• Subterranean nests (underground, in soil, stumps and tree bases)
• Tree wood (inside the tree)

Nest humidity and temperature maintenance

Termite colonies are maintained at a high humidity. This protects the thin-skinned workers from drying out. Only when the external humidity is close to 100% can workers leave the nest to forage. This is especially the case for subterranean termite species, which gain most of their water from the soil. These species can only become pests in buildings where a constant water source is available. Indoor plants on pavers are a major cause, as are leaking pipes or roofs). Termites that nest in dry wood don't have such strong water requirements and may attack wooden structures that are not necessarily very damp.

Nests are usually maintained at a temperature between 25°C - 36°C. This varies, depending on the species, the external temperature and the health of the colony. Healthy colonies are able to maintain this range during very hot and very cold external conditions.

Sometimes the nest shape is specifically designed to regulate temperature. The Compass Termite (Amitermes meridionalis) of the Northern Territory is known for its tall (3 m - 4 m) mound nests. These nests are thicker across their east-west axis (about 3 m) than along the north-south axis (about 1 m). This alignment means that the nest has the most protection from the hot summer sun as it moves east to west directly above the nest, but can still be warmed in winter, when the sun is at a lower angle.

Feeding and diet

Not all termites eat wood. Many species feed on grass and other matter, and are not pests in buildings. Those species that do eat wood, get cellulose, sugars and starches (all carbohydrates) from the sapwood (outer wood) of trees and can also eat any wooden structures, including logs, stumps and human constructions. They usually cannot eat the heartwood (innermost wood) as it tends to be much harder and can have toxins that repel the termites. Protein is obtained by eating fungi growing either in the humid nest - which also helps to keep the nest clean - or from moist wood surfaces.

Many termite species have special gut organisms that help them to break down the woody cellulose into sugars that can be digested. Some species have protozoa (single-celled organisms) that produce enzymes to digest the cellulose while others have bacteria. These organisms are transferred from termite to termite during grooming sessions, especially from adults to young.

Grass and spinifex-eating species are very important in the savannah ecology of Northern Australia. The large amount of biomass that they process makes them the equivalent of large mammals that eat grasses in similar savannah or prairie habitats in other parts of the world.

Other behaviours and adaptations

Castes

Termites have several castes that have definite tasks within the colony:

• Queen/s: there is usually one main (first-form) queen who may have been the original founder of the colony. She may be larger than other colony members and swollen with eggs. Queens can live and reproduce for a long time (up to 20 years in some species). There may also be several supplementary queens in a colony, which can take over egg production from the primary queen when she dies.
• King: the original king fertilises the queen and helps to tend the young during the foundation of the colony.
• Workers: with white-bodies and thin skin, these are the most numerous in the colony and are involved in food gathering, feeding and tending the young and the queen, and building or maintaining the nest. They rarely emerge from the nest or associated tunnels, as they dry up easily outside the humid nest environment.
• Soldiers: are the colony defenders. They are sometimes larger than workers, but mostly the same size, with darker heads. Two body forms are possible, with a particular species having one or the other: mandibulate (fully-jawed) and nasute (long-nosed). Some species also have two size classes - major and minor soldiers.
• Reproductives - both winged and wingless: these are the future kings and queens. Beginning as wingless nymphs, they develop by shedding their skin through several stages until they are fully winged adults. With darker, more durable bodies and compound eyes, they are able to survive for short periods outside the colony. They are destined to either leave the nest on a colonising flight or to take over from the queen if she dies.
• In some primitive termite species, there is no real worker caste, with the developing young taking on different roles as they moult. They may remain as undifferentiated workers, or moult into either a soldier or a reproductive form.

Termite Genetics Study

Needle in a haystack. This is a sequence of photographs showing what it takes to find and capture a queen termite from a termite mound. It was done as part of a genetic study into caste (worker, soldier, nymph etc ) determination in Coptotermes lacteus termites. C. lacteus are a common destructive species in Australia.

Life history cycle

Termites undergo an incomplete metamorphosis, with three developmental stages:

• Egg
• Nymph
• Adult

The eggs hatch into nymphs (the first instar) that are fed by the workers, and these nymphs then moult several times, differentiating into worker, soldier or reproductive forms. Development into adult forms takes several months, depending on food, temperature and the size of the colony. Hormones are thought to control the numbers of each caste, with imbalances corrected by nymphs developing into whichever form is needed at the time.

Breeding behaviours

Colonising flights

Termite colonies are formed when the winged reproductive forms leave their original nest and take a colonising flight. These flights occur during warm humid weather and usually take place during spring and autumn. The right combination of climatic conditions increases the chances of success in founding a new colony.

Starting a colony

Once a suitable site is found, the mating pair (the new king and queen) drop their wings, hollow out a small mating chamber, and the queen begins to lay a small number of eggs. Both the king and queen care for the young at this early stage. As the colony grows, the different castes take on their roles of workers and soldiers, leaving the queen to produce more and more eggs. She will produce 10-20 eggs in the early stages of a colony and may go on to lay over 1000 eggs a day after several years.

Economic impacts

Out of the 258 described (90 undescribed) termite species in Australia, only a few wood-damaging species are of concern to humans.

References

• Gerozisis R. and P. Hadlington. 2001. Urban Pest Management. University of New South Wales Press, 4th Edition.
• P. Hadlington. 1987. Australian termites and other common timber pests. UNSW Press.