Termites are insects of great economic importance since the chief food of a large proportion of the individuals is cellulose. In order to obtain this material they injure or destroy trees, crops, buildings as well as goods stored in the latter, thereby entailing immense losses to man, especially in tropical countries. Damage to wooden structures of all kinds is so extensive that the more progressive tropical communities are, where possible, replacing wood, especially below ground, by stone, concrete or iron. The nests or termitaria are very varied : the more primitive forms are wood feeders which construct no true nest but merely hollow out galleries in logs, decaying trees or manufactured timber. Other kinds burrow in the ground where they construct a labyrinth of tunnels either with or without mound nests above the surface. Among the higher termites, particularly those of Africa and Australia, the termitaria are often gigantic structures of great durability. They are formed of earth particles cemented together with saliva or with faecal material and, upon drying, the saliva-impregnated earth be comes of a cement-like hardness.
Some of the most remarkable of all termitaria are the lofty steeple-like structures constructed by Eutermes triodiae in north ern Australia, which are known to reach a height of loft. with a basal diameter of 12 feet. The interior of such a nest presents a maze of irregular chambers and passages while in its deeper re cesses the brood is reared and the royal cell, which will be men tioned later, is located. The compass or "meridional" termite (Hamitermes meridionalis) is widely distributed in Australia; its nests attain a height of 8 to i2ft., and are flattened from side to side in such a manner that the broad faces are directed east and west, with the narrow ends north and south. There are other termites which construct carton nests of chewed wood, placing them up trees; such nests are ovoid or rounded, and about the size of a football or larger, and consist of an outer envelope enclosing a comb-like mass of internal passages. Many termites, which have to come above ground in search of food or water, construct earth-like shelter-tubes or passages, which run up buildings or trees often to a great height and are very char acteristic features in the tropics. Secure in these covered ways they are able to travel long distances to and from their nests, pro tected from the daylight and from their enemies, but surrounded at the same time with the requisite humidity.
Caste development in termites, although strikingly like that of ants, reveals certain important differences. Among termites the sexes are of equal social importance, since each caste comprises individuals of both sexes, whereas in ants the workers and soldiers consist of female individuals only. In most termites there are five castes, three being fertile reproductive castes and two sterile. The reproductive castes consist of the following: (I). Normal winged males and females or macropterous forms (fig. 2) which have a firm dark integument and are usually known as kings and queens : the eyes and brain are large and the reproductive or gans well developed. The wings are ulti
mately discarded and only their persistent bases remain.
(2). Less pigmented brachypterous forms (fig. 3) with pad-like or incipient wing rudiments. The brain, eyes and re productive organs are somewhat smaller than in the first form.
(3). Scarcely pigmented apterous forms (fig. 4) with no traces of wings and with the eyes, brain and reproductive organs smaller than in (2).
The sterile castes are wingless and in them the reproductive organs are imperfectly developed and non-functional, except pos sibly at times in the most primitive species only. They consist of : (4). Unpigmented workers with the brain small and the eyes vestigial or absent (fig. 5). The head and mouth-parts are not exceptionally developed.
(5). Large-headed more or less pigmented soldiers with the brain small and the eyes vestigial. The mandibles are very large and projecting, varying in form in different species (fig. 6). In a few genera the mandibles are small and the heads retort-shaped, being drawn out into a rostrum bearing the opening of the large frontal gland at its apex : this type of individual is known as the nasute soldier (fig. 7).
Among the most primitive termites like Archotermopsis, Ter mopsis and Calotermes there are no workers and their functions are performed by the young soldiers and re productive forms. In some genera there are major and minor soldiers, and occa sionally intermediates also, while there are species with both large and small workers as among ants.
The origin of termite castes has given rise to much discussion and Grassi fol lowed by Jucci ascribe the differences be tween the several types of individuals making up a community to the influence of nutrition. Other authorities, however, have shown that, in some species at least, the young are separable into two types when they emerge from the eggs. Some individuals with small brain and eyes and with the reproductive organs in a very rudimentary condition, develop into ster ile workers and soldiers ; others with these several organs normally developed grow into fertile reproductive forms. Very early in post-embryonic growth further differentiation proceeds and all the future castes become recognizable by small differences exhibited by the young. In view of these facts it appears probable that among termites caste differences are due to intrinsic causes within the eggs, and are not modifiable by external influences. A remarkable feature in the lives of the more primitive termites which feed upon wood is the presence of enormous numbers of Protozoa in their intestines. Recent discoveries made by Cleve land, following upon the earlier observations of Bugnion and of Imms, indicate that the Protozoa are actually beneficial to the termites, apparently breaking down the wood devoured by those insects and rendering it in a condition capable of being digested. Cleveland has shown that by "sterilizing" termites of all Protozoa ' these insects are no longer capable of digesting wood and finally die, but if they be reinfected with these organisms their normal life and growth proceeds.