and antbears, already mentioned in the section on HOSTS, bolster this theory. Further indirect support is gained from the preva lence of the warthog's relative, the domestic pig, as a host. The tampan of human habitations may have evolved from populations formerly parasitizing burrowing, wild pigs, and they may still retain some predilection for pigs. As already noted, it is also possible that "wild" and "domestic" populations represent separate biological or physiological or even unrecognized morphological entities. Predators and Enemies Chickens, rats, and mice are said to feed on the eyeless tam pan, and ants carry off eggs and nymphs. An Angolan Reduviid bug, Phonergates bicolor Stal. sucks the blood of both man and 0. mou bata Wellman (1906B,D,1907B). Austen (1906,1907) reported on the nomenclature of this bug. The actual specimens involved may still be seen in British Museum (Natural History) collections_7. Ant lions (Neuroptera, Myrmelionidae) have been observed feeding on nymphs (Ghesquiere 1922). In the laboratory, larvae of clothes moths, Tineola biselliella, are said to feed on eggs and on living larvae of O. moubata (Volimer 1931). What was once described as a fungus disease beginning as an opaque white spot at one edge of the body and spreading out to stupify and destroy the tick (Wellman 1906A,D,1907B) is now be lieved by experienced workers to be a normal phenomenon of aging in engorged ticks. Christophers (1906) suggested that this "fun gus" is actually a white rectal secretion of aged ticks. Burgdorfer (conversation) is of the opinion that this "white fungus" is nothing more than crystallized fluid in the malpighian tubules. Often this crystallization produces a complete, hard blockage. The lumen of such tubules fills with white crystals so that normal activity can no longer occur and soon the tick dies. (See Internal Anatomy below). Numerous factors affecting the ecology of the eyeless tampan are discussed below. REMARKS Environmental Adaptability The xeric environment in which 0. moubata is capable of survival is best explained by two physiological studies by Lees (1946A, 1947). In his research on water balance in ticks, Lees (1946A) found that among the species studied, 0. moubata shows the greatest ability in limiting evaporation from its own body. In this species, the critical temperature at which water loss increases through the superficial waxy epicuticular layer is also high (Lees 1947). This resistance to desiccation at temperatures within its biological range may be correlated broadly with the argasids' choice of dry, dusty ecological niches. Lees summarized his 1946A studies, in which Ixodes ricinus was the principal species for research and O. moubata was one of eight other species used for comparative purposes, as follows: "The unfed tick gains water from humid air or from water in contact with the cuticle, and loses water by evaporation. Whilst attached to the host the tick is gaining water from the ingested blood and losing water in the excrement. The engorged tick usually lacks the ability to take up water from humid air. The exchange of water takes place mainly through the cuticle. Regulation of the water balance is there fore brought about by the activity of the epidermal cells. "The cuticle comprises two principal layers, the Water loss from the unfed tick is not closely related to saturation deficiency, particularly at high humidities. This departure is due to a physiological cause, namely, to the ability to secrete water. The effects of this activity are such that a state of equilibrium is attained at a relative humidity of about 92%; at lower relative humidities it takes up water. The retention of water at humidities below the point of equilibrium is due not only to the physical properties of the epicuticle but also to this secretory activity, for water loss increases when the tick is temporarily asphyxiated, poisoned with cyanide, or injured through excessive desicca tion. Near the point of equilibrium the loss or gain of water over a wide range of temperature is determined by the relative humidity. The uptake of water from humid air occurs when the tick is in a desiccated condition but ceases as the normal water content is restored. After previous exposure to saturated air the adapted tick at first loses water at relative humidities above the point of equilibrium, but later comes to retain water com pletely. "Both unfed and engorged ticks possess the abil ity to prevent or to limit temporarily the entry of water in contact with the cuticle. The engorging female, originally weighing about 2 mg., ingests about 600 mg. of blood. About 300 mg. or two-thirds of the contained water are usually eliminated before the end of engorgement. Evapora tion from the cuticle may account for a considerable fraction of this, for the temperature to which the attached tick is exposed (about 37°C.) is, in Ixodes ricinus, above that temperature at which a marked increase in the permeability of the epicuticular lipoid takes place. "The nine species of ticks examined differ con siderably in their powers of limiting evaporation. This may reflect specific differences in the nature of the epicuticular lipoid. The order of their resistance As already stated, Lees has shown that 0. moubata is more re sistant to desiccation than most ixodid ticks. Nymphs exposed to dry (R.H.) air at 25°C. survived for 35 days and lost only from one to three percent of their original weight daily. This survival period is strikingly longer than that of several ixodid tick species used in the experiments. After a period of desiccation (five days at % R.H.), O. moubata regains most of its original body weight when placed in 95% R.H. for five days. Water is taken up through the spiracles, for no increase occurred when these openings were blocked. Loss of water occurs through the cuticle and spiracles (see Spiracular Morphology and Function below). In order to carry Lees' work one step further, Browning (1954B) conducted a study on the exchanges of water between the atmosphere and 0. moubata. Unfed nymphs were able to abstract water from moist air 795% R.H. and to restrict their rate of water loss in dry air. This ability was lost (a) in atmospheres containing 30% to 45% CO2; (b) in atmospheres containing more than 90% N2; (c) immediately after the tick fed; and (d) gradually after the tick has been starved for some five months. It was shown that the action of high (30% to 45%) concentrations of CO2 is mainly upon the activity of the epidermal cells, possibly mediated through the central nervous system. The concentration required to cause opening of the spiracles is only about five percent. These findings are of considerable interest in relation to Lees' (1947) basic work. By way of introduction to his 1947 study, Lees stated: "In considering the mechanisms involved in the ex change of water through the cuticle the assumption was made that, in addition to active secretion, the passage of water, and particularly its retention, is also in fluenced by the presence of lipoid material in the cuticle. Ticks show great diversity in their powers of resisting desiccation, and this was thought to be accounted for by the specific nature of the waterproofing lipoid. Nevertheless, no direct evidence of such a component was ad vanced in this paper (i.e., Lees 1946A). "Ramsay (1935B), and more recently Wigglesworth (1945) and Beament (1945), have shown that the impermeability of insects is entirely due to a thin, discrete layer of wax or oil in the outermost part of the epicuticle. Any agents such as abrasive dusts, wax sol vents, or detergents, which interrupt the continuity of this layer, at the same time greatly increase transpira tion. Water loss through the wax layer is also enormously increased if the temperature is raised above a certain critical value. ..... methods devised by Wigglesworth for demonstrating the properties of the waterproofing layers in insects have been applied to a number of species of ticks. ...... observations on the structure and deposition of the epicuticle, and on the functions of the dermal glands (are provided). The outermost layer of the tick cuticle visible in ordinary sections has hitherto been referred to as the "tectostracum" (Ruser 1933) (but) the similarity of this layer with the insect epicuticle is so marked that the abandonment of this term seems fully justified."" The results and conclusions of this work, Lees summarized as follows: "1. Ticks owe their impermeability primarily to a superficial layer of wax in the epicuticle. After exposure to increasing temperatures, water loss increases abruptly at a certain critical temperature. The critical temperature varies widely in different species, in Ixodidae ranging from 32°C. (Ixodes ricinus) to 45°C. Hyalomma marginatum (= savignyi; and in Argasidae from 6300. |