192 MITES AND TICKS 



to penetrate the pericarp and consume the embryo. Grain that has 

 become damaged by water seeping into the holds of ships is often 

 attacked by another group of mites related to the forms that attack 

 flower bulbs, particularly in badly-drained soil, while if the grain 

 becomes completely saturated it may be infested with various 

 other species which can live completely immersed in water. 



Scabies of man is a condition produced by the itch-mite Sar- 

 coptes scahei which burrows in the skin where it lays its eggs, the 

 mite causing intense itching and irritation. In aggravated cases, an 

 extensive crusting and scabbing results, particularly over the hands 

 and arms. 



Oribatid mites live in moss, in the humus of the forest floor, in 

 lichens growing over tree stumps and trees, free on twigs and 

 leaves, in decaying wood and in the sphagnum of marshes. A few 

 are slightly aquatic and still fewer are known to inhabit the sea. 

 They are found everywhere that plants decay with sufficient 

 moisture and are penetrated by fungal mycelia (Willman, 1931). 

 A number of species are important as vectors of tape-worms of 

 sheep, etc. Apparently there is no taxonomic unit of mites that are 

 vectors; the determining factor is which species is dominant on 

 pasture and large enough to be able to swallow the eggs of the 

 worms. On the whole very little is known of the habits of the 

 Oribatei and there is much scope for further work. 



The curious excrescences and abnormal growths which occur on 

 the leaves and buds of plants are familiar to everyone. Various 

 creatures are responsible for these deformities, many being the 

 work of insects, but others are due to mites of the sub-order 

 Tetrapodili. Though the galls caused by these mites are often 

 outwardly similar to those of insect origin, they can at once be 

 distinguished on close examination. Mite-galls contain a single 

 chamber communicating with the exterior by a pore which is 

 usually guarded by hairs. The mites live gregariously within, 

 apparently feeding upon the hairs which grow abundantly on its 

 inner surface, whereas in insect-galls each insect larva lives in a 

 separate closed chamber. 



Food and feeding habits 



Mites live principally upon fluid nutriment, although this may 



