14 REPORT 108^ U. S. DEPARTMENT OF AGRICULTURE. 



man meet •with death Likewise many of the water mites will attach to adult insects 

 which leave the water, thus insuring their own destruction. This readiness to attach 

 to various hosts prevents the multiplication of species, and gives each a fair certainty 

 of life without the development of specialized characters. 



There are many curious cases of parasitism whose origin can only excite our won- 

 derment. The Dermanyssinse are parasitic on the skin of birds, mites, bats, etc. 

 But certain allied genera are internal parasites in very widely different animals; thus 

 one {Sternostomum) is found in the nasal cavities of certain birds, another (Halarachne) 

 in the bronchial passages of seals, and a third (Pneumonyssus) in the lungs of monkeys, 

 while an undescribed form I have seen is from the air sac of a snake. The few forms 

 of the small family Anystidse are predaceous and run very rapidly in search of prey; 

 but one genus has become parasitic'on lizards and snakes. 



We can only explain these remarkable habitats by the fact that mites, especially in 

 their immature stages, have an uncontrollable desire to go somewhere, and get into 

 every cavity and crack they discover in their wanderings. When hungr>' they test 

 their locality for food, and if not too different from their previous diet this new habitat 

 may result in new species and genera. 



Most mites ordinarily move quite slowly, but when disturbed some can travel at an 

 astonishing pace. A very few species are fitted for leaping. Aquatic mites occur in 

 both fresh and salt water. Ticks occur on mammals, birds, and even on snakes and 

 turtles. The bird mites live on the feathers and skin of birds; the itch mites burrow 

 within the skin of man and other mammals. Other species live in the cellular tissue 

 of birds; a few occur in the tracheal passages of seals, and several have been found 

 living within the lungs of monkeys. Many species feed on living plants, and the gall 

 mites produce curious deformations on leaves and twigs which attracted the attention 

 of the early botanists, who described them as new genera and species of fungi. 



Although mites are perhaps not as abundant in species as some would suppose, yet 

 by the enormous multitude of individuals they largely make up for their small size. 

 Trees infested by gall mites or red spiders may have many million specimens on their 

 leaves; an animal infested by mites may support thousands of individuals, and stored 

 food products attacked by tyroglyphids are often actually alive with immense hordes 

 of these pests. 



Mites are distributed throughout the globe, but appear to be most numerous in 

 temperate regions. The acarid fauna of countries outside of Europe is only A-ery incom- 

 pletely known, but from what is known it seems probable that mites are as easily dis- 

 tributed as any animals. Most of the exotic mites belong to genera well known in 

 Europe, but there are some remarkable forms, and, particularly in the Australian 

 region, there are peculiar genera. Most of the parasitic forms are* not confined to one 

 species of host, so that their range may be greater than that of any one of their host^. 

 Those occurring on domestic animals, on cultivated plants, or on foods become cosmo- 

 politan. Their minute size seems in no way to hinder their distribution. The exist- 

 ence of a migratorial stage in the Tyroglyphidcie and many Parasitid;r enables these 

 forms to spread very rapidly. Many forms are not easily susceptible to cold or mois- 

 ture, 80 they may extend far into the north and up high mountains'. The species 

 occurring in caves are mostly of the more primitive groups, as Eupodidae and Para- 

 si tidse. The mites found only under special conditions, as in ants' nests, are limited 

 in distribution. 



In Europe the English, Italian, and Dutch acarid faunas are fairly well studied: 

 and considerable is known of the French, German, Austrian, and Swedish faunas. 

 The forms that live in low and damp situations, as Eupodida\ Nothrus, etc., are com- 

 mon in northern regions, wliile those fond of drier places, such as Oribata and Rhyiicho- 

 lophus, are more abundant in the couth of Europe. The large family Parasitidic seems 

 to be fairly abundant in northern regions, but rather more numerous, and with greater 

 variety of genera in the south. The ticks are by far most numerous in the Tropics, and 

 very few species occur in northern localities. Some species of water mites occur in 



