- Key People:
- Alfred Edwards Emerson
- On the Web:
- CiteSeerX - Termites and microbial biological control strategies (PDF) (Mar. 01, 2025)
Cellulose
The food of termites is mainly cellulose, which is obtained from wood, grass, leaves, humus, manure of herbivorous animals, and materials of vegetative origin (e.g., paper, cardboard, cotton). Most lower termites and many higher ones feed on wood that is either sound or partly decayed. A few termites, known as foragers or harvesters, collect and eat grass, leaves, and straw. Many higher termites (family Termitidae) are humivores, or exclusively humus feeders.
As with other social insects, not all members of a termite colony feed directly. Because reproductives, soldiers, and young nymphs in lower families (all nymphs in Termitidae) cannot feed themselves directly, they must be fed by workers. Workers, or in families without them, the older nymphs, feed for the entire colony and transfer food to dependent castes either by mouth feeding or by anal feeding. Food transferred by mouth may consist of either pastelike regurgitated chewed wood and saliva or a clear liquid. This method is used in all termite families. During anal feeding, present only among lower termites, a pastelike liquid or droplet is discharged from the anus of the worker and licked away by the dependent castes. This liquid food, distinct from feces, consists of hindgut fluid containing protozoans, products of digestion, and wood fragments.
Cellulose digestion in lower termite families depends upon symbiotic flagellate protozoa, which live anaerobically (without oxygen) in the termite hindgut and secrete enzymes (cellulase and cellobiase) that break down cellulose into a simple sugar (glucose) and acetic acid. The termites depend entirely on protozoans for cellulose digestion and would starve without them. Newly hatched nymphs acquire protozoa from older, infected termites during anal feeding, a type of feeding necessary to lower termites that harbour protozoans.
Since the protozoans lost at the time of each molt are reacquired only through anal feeding, termites live in groups that allow contact of molting nymphs with infected, nonmolting individuals. It is possible that the necessity for transfer of protozoans was responsible for the evolution of the termite society.
Higher termites lack symbiotic protozoans, and only bacteria are present in the gut. Digestion may occur with the aid of bacterial cellulase and cellobiase enzymes, but in some species the termites themselves may secrete the enzymes.
In addition to cellulose, termites require vitamins and nitrogenous foods (e.g., proteins), which probably are supplied by fungi normally present in the decayed wood diet common to most termites. The fungi also may break down wood into components that are easily digested by termites.
Fungus gardens
The Macrotermitinae (family Termitidae) cultivate symbiotic fungi (Termitomyces). The termites construct spongelike “fungus gardens,” or combs, possibly of fecal matter rich in the carbohydrate lignin. The fungi grow on the combs, and the termites consume both fungi and combs. The fungi break down the fecal matter used to construct the combs into substances that can be reutilized by the termites. Nitrogen other than that from fungi is supplied by controlled cannibalism. The termites consume cast-off skins and dead, injured, and excess members of the colony.
Communication
Among the members of a termite colony there is continuous exchange of information, such as alarm, indication of direction and presence of a food source, and, among reproductives, calling and pairing behaviour. Information is communicated mainly by vibrations, physical contact, and chemical signals (e.g., odour). Visual cues may be used by individuals outside of the colony where light is present, but they play no role in the dark colony interior.
Many termite species leave their nests to forage for food. Workers (or older nymphs) and soldiers march in columns along the ground and carry grass, pine needles, and seeds for storage in the nest. The foraging trail between the nest and the food source may be indicated by deposits of fecal matter, covered runways over the trail, or pheromones secreted by a sternal gland as the termite drags its abdomen along the ground. The pheromone odour is detected by other termites through olfactory receptors.
Termites communicate alarm by vibrations, odour, and physical contact. Alarmed termites may tap their heads against the ground, quiver and jerk, or run in a zigzag fashion, bumping into other individuals. Although the vertical head-tapping movements produce rattling sounds audible to the human ear, termites cannot hear airborne sounds. It is the substratum vibration that they sense through the vibratory receptors located on their legs. The zigzag and horizontal jerking movements communicate alarm by contact; as an alarmed termite bumps into other termites, they, too, become alarmed. During this excitatory running, the alarmed termite leaves a scent trail, similar to the foraging trail, of pheromone that communicates direction and serves to recruit workers and soldiers to the point of disturbance.
Evolution, paleontology, and classification
Termites are related to the roaches and probably have evolved from a primitive roachlike ancestor. The most primitive living roach, the subsocial, wood-eating Cryptocercus punctulatus, which lives in rotten logs, has affinities with the termites. Cryptocercus harbours symbiotic, cellulose-digesting protozoans of the same genera as those found in the hindgut of primitive termites. The genitalia and certain internal structures of Cryptocercus have basic anatomic resemblances to those of the most primitive living termite, Mastotermes darwiniensis, from Australia. Mastotermes has further affinities with other roaches: its hind wing has a folded anal lobe, and its eggs are not laid singly as those of other termites but in clusters held together by a gelatinous material resembling the egg case of roaches.
Evidence of the relationship to primitive roaches suggests that termites evolved in the Late Permian (approximately 251,000,000 years ago), although the known fossil termites date only from the Early Cretaceous (about 130,000,000 years ago). The termite social system may be older than any other society. Ant social systems are estimated to be only 100,000,000 years old.
Classification
Termites of the order Isoptera are small to medium-sized insects that live in social groups, or colonies, and are characterized by their highly developed caste system. The mouthparts are modified for chewing. Antennae are moniliform (beadlike) or filiform (threadlike). Isopterans are very soft-bodied insects, usually light in colour. Head structures and the presence or absence of individual caste members are used to distinguish termite families.
Termites, although often called white ants, differ from hymenopterans (bees, ants, and wasps) in several ways. Termites have a hemimetabolous (gradual) metamorphosis and pass through a series of nymphal stages. Hymenopterans have the more common holometabolous metamorphosis, with distinct larval, pupal, and adult stages. Termite social castes (reproductives, sterile workers, and sterile soldiers) usually contain members of both sexes in equal numbers, and both males and females develop from fertilized eggs. In the hymenopteran colony, however, the sterile castes contain females only, with both sterile and reproductive females developing from fertilized eggs. Reproductive males develop by parthenogenesis from unfertilized eggs. The thorax in termites is joined broadly to the abdomen, without the “waist” characteristic of bees, ants, and wasps. Termites have two pairs of membranous wings, nearly equal in size, that break along a suture when shed, leaving only the wing base, or “scale,” attached to the thorax. This is probably the most distinguishing characteristic of isopterans.
Annotated classification
- Order Isoptera (termites)
- Highly developed caste system, may contain reproductives, soldiers, and workers; reproductives shed wings after mating; distribution worldwide, mostly in tropical rainforests; about 2,750 living, 60 fossil species; may inhabit moist subterranean or hot, dry locations; foods include plant cellulose, often digested by symbiotic protozoans in termite hindgut; all families (except Termitidae) known collectively as “lower termites” contain symbiotic protozoans in hindgut.
- Family Mastotermitidae
- Primitive; 1 living species (Mastotermes darwiniensis) in Australia; 13 Cenozoic fossil species worldwide.
- Family Kalotermitidae (dry-wood termites)
- Wood-dwelling, wood-eating; survive dry conditions; 292 living, 11 fossil species (some from Baltic amber).
- Family Hodotermitidae
- Thirty living, 13 fossil species (1, the earliest known termite fossil, from Lower Cretaceous, Labrador); includes rotten-wood termites and harvester termites that forage and store food in nests; Zootermopsis, largest termite in North America, found in Rocky Mountains at altitudes of 2,000 to 2,500 metres; Archotermopsis, found in Himalayas; Hodotermes species, serious pests of African grasslands.
- Family Rhinotermitidae (subterranean termites)
- Lives under damp conditions; 158 living, 13 fossil species; Reticulitermes, widely distributed in North America and other temperate and subtemperate regions and a serious pest; Coptotermes, a serious pest in tropical and subtropical regions.
- Family Serritermitidae
- One living species in South America; specialized family evolved from Rhinotermitidae.
- Family Termitidae (higher termites)
- Largest termite family (about 75 percent of all termites), 2,100 living, 3 fossil species; 4 subfamilies variable in morphology, social organization, and nesting habits.
