Termite Life Cycle & Behaviour

Although referred to as "white ants", termites are more closely related to cockroaches. They have a well ordered social system with amazing engineering capabilities and acute survival instincts. Apart from their habit of living in colonies, their resemblance to ants is purely superficial. There are over 1900 identified species of termites of which 350 occur in Australia and 30 species in particular are economically significant as timber pests.

Termites Can Be Grouped Into:

  • Dampwood termites which live in moist, rotting timber
  • Drywood termites which have no need for soil contact, obtaining moisture from timber
  • Subterranean termites which are primarily responsible for building damage Australia-wide are ground dwelling, and require contact with soil or a constant source of moisture

Termite or Ant?

Termites are pale brown to white, have beaded antennae and no constriction between the thorax and abdomen. Winged reproductives, (alates) have two pairs of equal sized wings and one pair of compound eyes. Workers and soldiers are blind, sexless and wingless, and have thin cuticles that are susceptible to desiccation in exposed environments. In contrast, ants vary from brown to black, and have an obvious constriction between thorax and abdomen. Their antennae are characteristically elbowed. Ant alates have two pairs of wings of unequal size and one pair of compound eyes. Ant workers, and soldiers have thick cuticles insensitive to desiccation so that they can exist outside the colony.

Termite V Ant Picture            Termite V Ant 2 Picture

The Termite Life Cycle

Termites metamorphose through egg to nymph to adult. By several moults, the young nymphs then differentiate into one of several castes. This may take several months, depending upon food availability, temperature, and the colony's vigour. Within a termite colony there are several forms (castes); namely a queen, king, workers, soldiers, and periodically, reproductives. Each caste is structurally different with specific functions to perform for the colony's survival and maintenance.

Termite Life Cycle Picture   Termite Life Cycle 2 Picture

Termite Castes

The Queen & King

They are the original winged reproductives (alates) which left the parent colony during the colonising flight. They then shed their wings to seek out a suitable nesting site, mate and establish a new colony. Their function in the colony is reproduction - the queen becomes an egg laying machine of over 1,000 eggs per day. Colonies of different species vary in size from hundreds of thousands to millions of individuals. For destructive species to reach a damaging stage from a single pair usually requires 3 to 5 years, depending on the site, food and immediate climatic conditions.

Both queen and king may live for over 25 years. As the queen ages, her reproductive capacity declines, and the colony may then select supplementary queens (neotenics) from the various developmental stages of reproductives to replace the queen and king. These reproductives never go on a colonising flight.

Workers

These numerically dominate the colony since they perform all tasks including gathering food, tending the eggs and feeding the young, building the nest and galleries, repairing damage, and tending and feeding the queen with the exception of defence and reproduction. Workers are responsible for timber damage and construct earthen leads as they search for and excavate timber. They are wingless, blind and sterile, and have thin cuticles or body covering making them susceptible to desiccation outside the colony. Older workers may predominate in activities outside the nest. Workers leave the security of the colony via underground tunnels and shelter tubes only when the humidity is high. In some species, larvae develop into workers or nymphs. These workers may then develop into soldiers and the nymphs may become alates. In other species, the worker caste remains as workers throughout their developmental stages.

Nymphs

In some species there is no true worker caste. The developing nymph moults until it reaches an advanced stage of growth and then does the work of the colony. At this stage it can continue to feed and moult without differentiation or moult to a pre-soldier and then soldier; moult to a reproductive nymph with wing buds and then to an alate or form reproductives in the same colony. Other species do not have such a versatile nymphal stage, but have distinct workers, soldiers and reproductives determined very early in their nymphal development.

Soldiers

The soldier caste is the easiest from which to identify the species. They tend to be abundant where there is a large central colony. Like workers, they are wingless, sterile and blind. However, they are usually darker in colour and are distinguished from other castes by their heavily armoured and pigmented heads. Because their mandibles are so specialised, they must be fed by workers. Soldiers are also susceptible to desiccation and seldom leave the environmental security of the colony and shelter tubes.

Two Physically Different Types of Soldiers

  • Mandibulate with obvious, large jaws
  • Nasute with a large head that tapers abruptly to a point

In some termites, two size classes of soldiers may be present i.e. majors and minors. These often differ in physical characteristics as well, and the numbers of each vary as colonies age.

Several species have a frontal gland that discharges a secretion through a pore in the front of their head. This secretion is associated with defence, being repellent to ants and other enemies. The colour and nature of this secretion are sometimes characteristic of the termite species aiding in identification. The soldier's role is solely defence of the colony with their large heads, jaws and chemical secretion.

The Colonising Flight

During the colonising flight fully winged reproductives leave the colony annually through "blow holes" or "flight cuts" when external temperature and humidity approximate conditions inside the colony, often before or after a storm usually in the warmer months of November and December. After the flight, the tree calluses over these slits. Because alates do not fly strongly, their dispersal is assisted by winds. They normally swarm at dusk and are attracted to light. Swarming termites are a sure danger sign that a mature termite colony nest is close by. In some species, new colonies are established without a colonising flight. These reproductives mate and produce young, developing large colonies.

 Termite Alate 3 Picture         Termite Alate 4 Picture

Food

Most termite species feed on leaves, bark, and grass, the attractiveness of which is improved by decay. Termites of economic importance eat cellulose, starches, and sugars obtained from wood. Contrary to popular belief, termites are fussy eaters. They do not attack all wood and the wood that is attacked is not attacked equally. Different timber species have varying resistance to termite attack due to the palatability of the timber, the presence of distasteful chemicals in the wood or the wood density which slows the speed at which termites can chew it. Sapwood is preferred to heartwood as the latter has less food value, is more durable and may include toxins. Only a small number of termite species eat sound wood but no timber is "termite proof".

Termites obtain their protein from fungi growing in or on wood in moist conditions, particularly where ventilation is poor and humidity is high. Many termites have tiny single-celled protozoa in their intestinal tract. They produce an enzyme that digests cellulose which is essential in the conversion of cellulose to soluble sugars. Other species have intestinal bacteria. Both protozoa and bacteria contain nitrogen so that by disposing of excess, dead and diseased members of the colony by cannibalism, termites are able to conserve nitrogen. Bacteria or protozoa are also transferred from termite to termite via feeding and grooming.

Most subterranean termites forage for food by means of galleries usually in the top 20 cm of soil or shelter tubes extending from the central nest. This gallery system may exploit food sources over as much as a hectare with individual galleries extending up to 50 meters, depending upon the species, soil type, available food sources, and moisture content. Usually only workers and soldiers visit the feeding sites - the other castes remain in the nest. Foraging activity is seasonal, slowing in winter. Although exploratory foraging is thought to be at random, termites tend to aggregate in warm, moist areas containing susceptible timber.

Climate: Moisture & Temperature

Being susceptible to desiccation, termites require a continual supply of moisture and maintain their nests at nearly 100% humidity. They use moisture from the soil to maintain the colony's humidity and evaporation to regulate its temperature between 25C and 36C, depending upon the species and prevailing weather conditions.

Subterranean termites can survive without soil contact, but must have an assured and constant moisture supply. Termites favour decaying wood in moist situations within which to establish colonies as it provides them with protein and moisture.

Termite Nests

Nests built by workers are often characteristic of the species, aiding in identification when considered with features of the soldier caste. Nests may be ground mounds of various shapes and sizes; tree or arboreal structures; subterranean colonies in the soil; or small colonies in dry wood, trunks and branches of trees. Species which have subterranean habits may nest inside living trees and dead stumps, under verandahs, or concrete slabs.

Ground Mounds

These may be of various shapes from tall upright mounds to more robust, smaller mounds to low dome-shaped mounds with an internal and external structure characteristic of the species. The outer layers protect the softer, often papery, inner central nursery area which houses the queen and developing nymphs. Mound-forming species attack timber in the ground by making tunnels through the soil radiating from the colony.

These have ground contact usually through the root crown of the tree. They are often large, occasionally attaining heights exceeding 20 meters. By subterranean tunnels and shelter tubes, they attack decaying weathered timber and may be capable of doing considerable damage in a very short time to buildings within at least 50 meter radius of the tree.

Subterranean Nests

Many species have colonies below ground surface created when building covers tree stumps, roots and waste timber providing decaying wood in a moist situation, often under verandahs and in-fill used under bathrooms.

Nests in Root Crowns and Trunks of Trees

Existence of these colonies is often very difficult to detect. However, these colonies may be capable of doing considerable damage within months to buildings within at least 50 meter radius of the tree.

Termites are grouped according to nesting behaviour

Single-site nesters e.g. Drywood and Dampwood termites cannot burrow through the soil and live their entire lives inside a single piece of wood.

Multi-site nesters e.g.Heterotermes sp, Schedorhinotermes sp andMicrocerotermes sp burrow through soil to find food. They may establish or bud off new nests if they locate a large food source.

Central-site nesters e.g. Coptotermes sp also burrow through the soil, but they always transport food back to their original nest which is very large and complex.

Multi-site and in particular, central-site nesting termites show seasonal foraging patterns. Foraging is greatest in warmer, summer months and least in cooler winter months. This pattern varies with the distance from the nest so that foraging is higher in feeding sites further from the nest in summer and lower in sites closer to the nest and the converse for winter. Similarly, there are daily foraging patterns. Foraging activity is highest at the warmest time of the day and lowest at the coolest time of the day especially in winter with forager numbers peaking in the middle of the day. In summer there is a drop in numbers, especially for central-site nesters around the middle of the day.

Termites do not have a clearly delineated territory in which they operate. It is not unusual to find two colonies feeding in the same piece of timber due to colony overlap which explains why active termites may reoccur within previously infested galleries a few months after a colony has been eliminated.

Termites like to travel along predetermined tracks along environmental gradients; they prefer to traverse through damp or warm soil following clues from soil micro-organisms. They randomly forage for a larger food source they can frequently return to.

Many people refer to finding "nests" in cavity walls although this is rare. To be considered a termite nest there needs to be a reproductive pair present, eggs, nymphs, and reproductives. Instead, these areas of intense mudding in cavity walls are really food stores, resting points or bivouacs. Termites may consume food at this point but they are more likely to seal it off and leave it as a future food store.

Concealment is the primary way termites defend themselves because they have weak, soft exoskeletons and short legs. Termite mud tubes allow them to move safely between places. Soldiers are the secondary defence mechanism of the colony, fending off invaders long enough for the workers to wall off the part of the colony being attacked, sacrificing soldiers in the process. Because of these weaknesses, termites normally avoid areas that are in constant use. In the case of most termite dust toxicants, the colony can detect the presence of the toxin and seal off that part of the colony, effectively sacrificing themselves so that the nest survives. This is why dust treatment often gives short term success with termites appearing again a few months later. When faced with a threat, termites send out a warning signal to the rest of the colony by convulsing, banging their heads and producing vibrations that the rest of the colony interprets as a signal to evacuate.