Isoptera (termites, white ants)

Fast facts about Isoptera (termites)

  • Mainly tropical, 2,500 plus species world wide, only 12 species native to Europe.
  • in the tropical rainforest there can be more than 1,000,000 termites in a hectare.
  • Social insects with different castes.
  • Colony size from thousands to millions.
  • Hemimetabolous.
  • Most less than 20 mm long, but queens can reach 150 mm long.
  • Often called "social cockroaches".
  • Descended from wood-eating cockroaches.
  • Castes contain both males and females.
  • Most eat wood, some eat grass and fungi.
  • Soldiers and reproductives are fed partly digested food by workers.
  • Workers also produce partially digested faecal pellets containing the bacteria which break down the tough cellulose of plant cells.
  • They have short antennae.
  • Only the king and queen have wings, and these break off after the nuptial flight.
  • These wings are longer then their entire body length.
  • Both rear and front wings are similar (see drawing below), Isoptera in Greek = equal wings.
  • Compound eyes are present in reproductives, but may be reduced or absent in the workers.
  • Most have soft, pale-coloured bodies with short cerci.
    Most species have biting mouthparts.

Similarities between termites and social Hymenoptera.

  • The caste system.
  • Trophallaxis - exchange of food - is important in social organization.
  • Chemicals are used in communication, e.g. trail laying, and recruitment.
  • Pheromones control the caste system inhibiting the production of reproductives.
  • Grooming is common and is one means of transmitting pheromones throughout the colony.
  • Individual nests have their own odour and territory.
  • Both have the ability to regulate the nest environment, e.g. temperature and humidity.
  • Cannibalism occurs in some.

Differences between termites and social Hymenoptera.

  • In Hymenoptera the caste is primarily determined by the food fed to the larva. In termites it is determined primarily by pheromones.
  • In termites the workers are both males and females; in Hymenoptera the workers are all female.
  • In termites the older nymphs work; in Hymenoptera the larva are helpless grubs, and all the work is done by adults.
  • Social parasitism between species is fairly common in Hymenoptera, but is absent in termites.
  • In termites the exchange of liquid anal food is common; in Hymenoptera it is rare.
  • In termites the male reproductive (king) stays with the queen after the initial mating and helps construct the first nuptial chamber. Also he fertilizes her on a number of occasions as the colony develops. In Hymenoptera the male fertilizes the queen during the nuptial flight and dies soon afterwards. He plays no part in nest searching or construction.
Termes bellicosus, termite, sexual with wings

Left is a reproductive of Termes bellicosus in the Termitidae family.

Termite Nest

After mating the king and queen construct a nuptial chamber. This is the start of the termite nest.

The mass release of king and queen termites from the nests usually occurs in the late afternoon or early evening, often when the ground has been softened by rain. The air is filled with insects that look as if their wings are too large for them and their flight is weak.

In the eighties I lived in rural Japan and used to watch them as I returned home from work on the train in the evening. When we stopped at small country stations the doors were left open (no air-conditioning in those days), the light would attract the termites and in they would flood. The smooth floor confused them and in an effort to rid themselves of their wings they would try to back into the nearest obstacle; this was usually the metal rail going from floor to ceiling. The floor would be covered in wings, and if the termites were in luck they would be blown out at the next station and not have to carry on to the concrete covered terminus.

For most species, in time the nuptial chamber also becomes a prison. It is enlarged by the workers as the queen grows, but the tunnels leading off the nuptial chamber are not big enough for the queen to pass through. Some African and Australian species construct huge mounds and towers reaching as high as seven metres.

Amitermes atlanticus from egg to adult

Termite king and queen

The king and queen can live as long as 50 years. They mate frequently in the nuptial chamber. The queen can grow to be as long as 10 cm, the the Termes flavipes queen on the right. If the king or queen die the workers simply rear a new one.

Termite soldiers

Soldiers tend to have large heads. Some have large jaws, and others have a nozzle through which they can squirt poisonous, repellent or sticky liquids depending on species.

In some species the soldiers have defensive saliva; there are 2 types: 1) the saliva is converted as it reaches the air into a rubbery substance that entangles small predators 2) a mix of saliva that forms a resin that again entangles small predators such as ants.

Most soldiers lack functional eyes. It is thought that soldiers and workers could live for up to ten years.

Regulating termite caste numbers

Workers produce a "worker substance" pheromone, and soldiers produce a "soldier substance" pheromone. If the level of either pheromone falls below the appropriate level more individuals of the appropriate caste are produced in the next generation.

Thoughts on the origin of social behaviour in termites.

  • Termites depend on symbiotic intestinal bacteria to help them digest their food.
  • The hind gut is enlarged to form a sac which contains the cellulose-digesting bacteria.
  • It is the products of the bacterial digestion that are absorbed by the termites.
  • The bacteria are passed on to the young during anal feeding.
  • When a nymph moults part of the gut lining is lost and along with it the symbiotic bacteria.
  • Anal feeding can help top up the supply of symbiotic bacteria.
  • Anal feeding requires some degree of social behaviour or co-operation, and it is believed that this paved the way for further and deeper social behaviour.

Termites in the UK

In 1994 a Reticulitermes grassei colony was found in a house in North Devon. The colony was eradicated, or so it was thought, but 10 years later the same species was found in the area.

Termes flavipes queen, termite queen
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