MITES AND TICKS 191 



of oceanic islands. On a dry, stony path on a sunny day in this 

 country, one often find the adults of scarlet velvety mites Throm- 

 bidium sp. running about and feeding on small insects and their 

 eggs, v^hile others are common in leaf litter and under bark. 



Much attention has recently been directed toward the biology of 

 the minute hexapod mites vs^hich for ages have plagued man in 

 various parts of the world, and which are known popularly as 

 'harvest bugs', 'harvest mites', 'bete rouge', 'rouget', 'chigger 

 mites', etc. Great difficulty is usually experienced in obtaining the 

 complete life history of these mites as the larvae alone are parasites. 

 Jones (1950a) has investigated the sensory physiology of the harvest 

 mite Thromhicula autumnalis. These animals are attracted to light 

 and to moist air: they are very sensitive to touch but not to tem- 

 perature although a range extending from 15° to 26° C appears to 

 be preferred. The gregarious habit of the mites is primarily a 

 response to the touch of each others bodies. The food of the harvest 

 mite, Thromhicula autumnalis, consists of tissue, fluid and dis- 

 integrated cells of the malpighian layer partially liquefied by the 

 action of injected saliva, a condition typical of extra-intestinal 

 digestion. The physical factors of the skin have been shown to 

 influence the choice of habitat upon the host. On birds the mites 

 appear to favour the anal area and the lateral surface of the body 

 between the wing and the thigh; but on man the factors which 

 influence the choice are more varied, regions where the skin is thin 

 and which provide the warmth and humidity favoured by the 

 larvae being most likely to be attacked (Jones, 1950b). 



Like the Thrombidiidae, the Acaridiae are notable for the extent 

 of their distribution. They are found in all types of habitat from 

 arctic tundra to tropical rain forest and wherever man in his 

 wanderings has taken mites in his food and produce. Of the species 

 attacking stored food, Tyroglyphus farinae is by far the most 

 important. It infests all kinds of farinaceous material, not only 

 eating the food but giving it a curious musty smell and taste so that 

 it becomes unfit for human consumption. Not only is this species 

 found in warehouses, but it also occurs in the nests and fur of 

 small rodents which act as a natural reservoir of the mite. Grain 

 which has become attacked by weevils or damaged mechanically 

 is made more readily accessible to flour mites which are then able 



