Termites (Insecta, Isoptera), together with Hymenoptera (ants and bees), represent the only group of insects with socially organized communities. It is precisely this social organization that is responsible for termites' complex and fascinating biology (a wide variety of structures and physiological processes, symbiotic relationships with micro-organisms, social behaviour, differentiation and regulation of classes, etc.). Similarly, and in conjunction with the cryptic habitat in which they reside and their competitor-free exploitation of certain resources (wood), the social structure of their communities facilitates this group of insects a very high biological potential.
Biology and social organization of communities
Termite communities live in underground nests (termitariums) hosting four different morphological groups (casts); the primary reproductives (royal couple), the supplementary reproductives, the soldiers and the workers. Termite colonies are composed of a royal couple, various supplementary reproductives, a large number of workers and soldiers and a group of immature individuals in various phases of development (nymphs). Nymphs emerge equipotent from their eggs, with their future cast being determined by a series of social and environmental factors.
The new winged individuals of both sexes which are produced within the colony abandon the termitarium in search of partners. The new couples then shed their wings and begin the construction of a small cavity in which the female is fertilized before laying its eggs. The first nymphs to emerge from the eggs are fed by the mother prior to their transformation into workers responsible for the construction of the definitive termitarium and for feeding the parents and the nymphs born in subsequent generations. During the initial phases of the new termitarium, only workers are produced. Once their number has grown, soldiers are produced in order to defend the colony. Finally, the supplementary reproductives emerge.
The queen soon ceases to work and to feed herself, with these tasks being taken over by the workers. Once having reached this stage, the queen is capable of dilating her stomach to a considerable degree in order to increase her egg-production capacity. Together with the royal male, she remains immobile within the royal chamber, exclusively dedicated to laying eggs. The formation of the different casts is determined by pheromones emitted by the reproductive couple and transmitted to all the members of the colony.
The development period of termites varies in accordance with the species and the cast in question (it is longer for the reproductive casts than for the sterile casts) although, in general, the period which lapses between the ovipostion and the emergence of the adult varies between four and six months.
Termites in Spain
Of the more than 2,200 species of termites recognized throughout the world, only some 4% cause problems within urban environments. Only four species of termite have been detected in our country: Kalotermes flavicollis (Fam. Kalotermitidae), which is native to the Mediterranean region; Kalotermes dispar, a species which is endemic to the Canary Islands; Cryptotermes brevis (Fam. Kalotermitidae), originally from the Caribbean, Central America and South America and which was introduced by man via the Canary Islands; and Reticulitermes lucifugus (Fam. Rhinotermitidae), which again is native to the Mediterranean.
The first three mentioned species belong to the ecological category of dry-wood termites, whilst Reticulitermes Lucifugus, the most commonly-found species in the Iberian Peninsula, belong to the ecological category of subterranean termites.
Reticulitermes lucifugus is widely present throughout the entire Mediterranean area. It nests are inhabited by many thousands of individuals. This species is usually found below the stumps of old trees, as well as under wooden fence posts, wooden telegraph poles and wooden constructions in general. New colonies can be formed by a single pair of winged adults, which become the king and the queen of the future termitarium, or by a part of an existing colony which separates from the main community and produces its own supplementary reproductives. Winged adults leave the termitarium in swarms during warm, sunny days between the months of April and June.
The workers of the Reticulitermes species travel up to 30 metres from their nests in search of food and create underground tunnels and galleries in different types of materials.. However, they are unable to perforate hard materials (rock, metal, etc.), and are thus forced to come to the surface. In such cases, they construct exterior galleries from chewed wood and agglomerated faecal material, which provide protection from exterior threats and enable them to reach food sources and return to the nest unharmed with their finds. Although subterranean termites usually feed onthe dry wood of dead trees and wood used for construction, they occasionally consume live vegetable tissue and their activities are capable of killing a wide rangeof tree species.
Damage caused by termites
Although termites may occasionally cause damage to crops (fruit trees and, especially, vines), forests and ornamental trees, in this section we are going to focus on the damage they case within urban environments.
Within this context, termites are capable of causing damage to wide range of materials in their search for food, including not only wooden structural elements (beams, floorboards, panels, window- and door-frames, etc.) and household furniture, but also all types of wooden and paper wall-coverings and material containing cellulose (paper, books, cardboard, certain types of fabric, etc.).There are many other types of non-organic materials which termites are capable of damaging, even when they are not consumed as a food source. Although termites are unable to digest the synthetic fibres used for making many types of fabric, the workers often damage such materials by creating holes and galleries when exploring in search of new food sources. These insects also attack the protective piping of electrical and telephone cables, giving rise to the danger of short circuits and the interruption of telephonic communications.
The damage caused by worker termites in search of food is accompanied, to a lesser degree, by the problems caused by reproductive winged termites when leaving the nest in swarm formation. Such flights can interfere in the activity of public centres (offices, schools, etc.) and even lead to the contamination of food and other products. Nevertheless, the flights of the winged reproductive termites are capable of playing a significant role in the control of these insects, given that their detection is usually the first sign of a termite attack and, consequently, the first indicator of the need to introduce control measures.
Damaged caused to wood by Termites
Social organization of termites
The primary reproductives are winged individuals with a fully-developed reproductive system. They are slightly darker than the termites belonging to other castes as a result of a harder integument. In suitable environmental conditions, the new alates produced in the colony leave the nest in swarms before dispersing and forming new reproductive couples. The primary reproductives are responsible for founding colonies and, as such, possess a complex behavioural repertoire that is exclusive to their caste. The royal couple control the community's social structure by means of pheromones which inhibit the formation of new supplementary reproductives, soldiers and workers.
The supplementary reproductives have smaller wings, or are wingless, and their integument is neither as dark nor as hard as that of the primary reproductives. They only appear once the population of workers and soldiers has reached a certain size. They transform into primary reproductives when a substitute pertaining to this caste is required or in the event of a part of the colony becoming isolated from the influence of the royal couple.
The soldiers are specialized in the defence of the colony. They have strongly pigmented, sclerotized heads with very large jaws. The soldiers, which depend on the workers for food, do not have a developed reproduction system.
The workers are sterile individuals -male and female - without a developed reproductive system. Although they are similar in appearance to the nymphs, their work consists of providing food, caring for the young and constructing the nest.
This special type of termite has stable nests or reproductive centres, which are usually found underground and from which the workers leave in search of food. These termites require a greater degree of humidity than that available in wood, and which they obtain to a great degree from the earth. They also seek humidity in form of leaks from water pipes, condensation, etc. Whilst humid- and dry-wood termites form small colonies exclusively within wood environments, subterranean termite colonies are usually far larger and are composed of one or more - interconnected - reproductive centres (containing several queens). Due to the large size of the populations, the damage caused by these termites is far greater than that caused by the groups mentioned above.
Termites in Spain
Of the more than 2,200 species of termites recognized throughout the world, only some 4% cause problems within urban environments. Only four species of termite have been detected in our country:
Kalotermes flavicollis: This species is found in the more humid regions of the Mediterranean region. It lives in communities of between 1000 and 1500 members. It does not have a true workers caste, with nymphs in their final phase of development carrying out the tasks of gathering and distributing food among the community. Its termitarium consists of galleries excavated from the wood. The queen, which never develops a hypertrophied abdomen, occupies a wide gallery - which serves as the royal chamber - together with the royal male. In normal conditions, its development is slow and subject to seasonal fluctuations: the egg-laying, feeding and growth processes are halted in cold weather. New winged members only appear some two years after the establishment of the colony. Its natural habitat is the interior of dead or ailing tissue, generally close to the limit with healthy wood, of vines and a variety of trees (oak, holm oak, elm, fig trees, olive trees). Nevertheless, this species has also been identified as the cause of damage to healthy trees. Similarly, in sufficiently humid conditions this species may live in dead trees and structural wood in buildings.
Kalotermes dispar: There is very little information available about the biology of this species, which is endemic to the Canary Islands. However, in general terms, it coincides with that of the previously mentioned species.
Cryptotermes brevis: This is one of the most widely-extended termite species, having been introduced into various continents by man. Within the context of Spain, C. brevis was introduced into the Canary Islands, where it became established. Perhaps one of the factors that have aided the dispersion of this termite is the fact that it lives in very small colonies - the number of members rarely exceeds 300 -, together with its capacity to live in extremely dry wood, structural wood and small items of furniture, which facilitates its transit through goods.
Reticulitermes Lucifugus: We have already covered this species extensively in a previous section.