Termites are the only members of the insect order Isoptera. There are more than 300 species found in Australia but only about 30 could be considered to be pests of timber in service. Of these, the subterranean termites are the most significant, with about 12 species being serious pests. The termite diet is centred around cellulose-based materials. These can include the timber used in constructing buildings but could also include furniture, paper materials and fabrics. These termites can also damage non-cellulose materials such as polystyrene and plasterboard or the plastic coatings on electrical wiring.
Life History and Habits
Termites are social insects and live in colonies containing a number of different castes. Each caste has a different form and function from the others; each is vital to the viability of the colony. In general terms the life history of all the economically important subterranean species is similar.
On a warm, humid evening large numbers of winged male and female termites, the “alates” or “primary reproductives”, are released by the colony. A small number survive the flight, drop their two parts distinctive, equal sized wings, pair off, mate, and if they can find a suitable location, start a new colony.
As the other castes take over the running of the colony the young queen of most species becomes “physogastric” – her abdomen distends to many times its original size and she becomes an egg laying machine, laying up to 1000 eggs per day. She is confined to her royal chamber, tended and fed by the workers and regularly fertilised by the male reproductive.
The eggs are removed from the royal chamber and transferred to a nursery by the workers. Here the brood (the eggs and nymphs) develop into the other castes that the colony requires for development and survival; workers, soldiers and primary or secondary reproductives.
Soldiers and workers are blind and sterile termites. The workers carry out the work of the colony and are responsible for gathering the food the colony needs. In most species, the heads of the soldiers are uniquely armoured and equipped to allow them to defend the colony against attack, notably ants.
Coptotermes Acinaciformis is found throughout mainland Australia and causes more damage to property than any other species. It is aggressive in its search for food and will attack many items other than wood in its search for cellulose materials. It will damage wall lining boards, electrical wiring and even personal possessions. Colonies often nest in trees or stumps but can form sub nests or secondary nests without ground contact.
There are several species of Nasutitermes which may damage timber in service. Soldier termites of these species are distinguished by their pointed heads. Nasutitermes exitiosus usually builds a low mound and is more common across Southern Australia. Nasutitermes walkeri builds part of its colony as a nest on the branch of a tree; the rest is constructed in the ground beneath it. This genus will mainly attack hardwood such as that found in fences and timber decking.
Mastotermes darwiniensis, the Giant Northern Termite, is the most primitive of the commercially significant species. It shows an ability for sub-colonies to split from the main colony and produce queens, without a mating flight. Eventually a network of interconnecting sub-colonies is established, which makes control difficult. These large termites can devastate buildings, bridges, poles, trees and crops such as sugarcane. Mastotermes is found mainly north of the Tropic of Capricorn.
These termites can cause damage approaching the severity caused by Coptotermes. They build fragile nests in places such as old tree trumps, in timber buried in the ground, in filled patios and under fireplaces. The damage they cause is distinctive. Although it can be severe it is often patchy, with huge gouges taken out of sound timber, particularly around nails in floor boards or other timbers. Schedorhinotermes colonies contain major and minor soldiers.
Heterotermes spp. Are a significant structural pest through Queensland, northern WA and the NT. It is only in southern Australia where they are a minor nuisance. They are generally considered to do little damage to timber in service, restricting their attention to weathered timber fences, decking and posts. Occasionally they can cause superficial damage to sound timber.
Termites build a nest that contains the queen and king, the nursery and a large proportion of the soldiers and workers. Some species build a hard-shelled mound above or partly below the ground. Others build their nests in the trunk of a tree or below ground in the root crown. A nest can contain several million termites.
Habits and Damage
The nesting habits of subterranean termites can be described in two basic groups:
1. Multi-site nesters (Heterotermes, Schedorhinotermes, Mastotermes)
2. Central-site nesters (Coptotermes, Nasutitermes)
Multi-site nesters utilise many timber sources for nesting and they can move quickly to a new food source. They are able to reproduce quickly using “ergatoid” or multiple reproductive forms so each new timber source located becomes a potential nest. These species can therefore set up multiple colonies within the same house.
Central-site nesters generally have one large queen and a central nest position. The activity of the colony is to bring back food to this nest. They can infest multiple timber food sources but cannot reproduce within those timbers. When a moisture source is available within a house structure, central-site nesters often establish their colony inside the building without any ground contact.
Central-site nesters show definite seasonal variation with their foraging behaviour. Generally, foraging activity is greater in the warmer months and reduced in cooler winter periods. The available moisture can also limit the foraging activity of these species. Generally distant food sources show greater foraging activity in warmer periods and food sources close to the nest are more active in the cooler months.
Multi-site nesters do not have the same restrictions as they can move their nest to adjacent food sources. This type of foraging activity often leads to splitting of one colony into several distinct colonies within the same area. The activity of these species quickly multiplies in a disturbed environment such as recently cleared land or fire damaged property.
Termites are prone to desiccation. All significant species that attack buildings construct a system of sealed leads that connect the nest to the food sources. Termites can move safely from the nest to the food and back, in an environment that will protect them against exposure to atmospheric conditions, predators and even pesticides.
Damage to timber and other materials
Timber is the main source of cellulose sought by the commercially important species. Sometimes other, non cellulosic materials are damaged because they are close to feeding activity. Electrical wiring, switches and plug fittings are often attached and severely damaged by termites. When natural food supplies such as trees run out, the termites will turn to timber in service. Using covered mud tunnels to link the food supply to the nest, termites will work in timbers that are hidden in floor, wall or ceiling spaces and the damage is often not discovered until structural failure takes place or the termites reveal themselves in some way. Termites can cause extensive damage and more than one colony may attack a building at the same time.
In order to minimise the extent of termite damage it is recommended that regular inspections be carried out by a competent and experienced termite inspector.