MITES AND TICKS 199 



the adult. During copulation the male crawls under the female 

 from the rear and clasps his front legs about her abdomen and his 

 second pair of legs about her hind legs. He then curves the end of 

 his abdomen upward and forward until it meets the end of the 

 female's abdomen. Copulation lasts from ten to fifteen minutes. 

 Eggs are laid within a day or two days of emergence in hot weather: 

 these summer eggs do not show diapause and hatch in about eight 

 to ten days. The number of generations in a year depends on 

 climate and latitude. Over-wintering, diapausing eggs are laid 

 towards the autumn, their production being engendered by the 

 decreasing length of daylight until cold weather kills the adult 

 mites or causes the leaves on which they are feeding to fall (Lees, 

 1955). 



The conditions of the micro-environment under which many 

 parasitic mites can multiply are often limited. Thus 12° to 14° C 

 represents the lowest temperature at which Liponyssus bacoti can 

 reproduce and then only with a great lengthening of the cycle and 

 an increase in mortality, and many other species that normally feed 

 on the body of their host where they are protected from the cold 

 are restricted in a similar way. 



Most of the Cheyletidae and Demodicidae develop normally 

 from tgg, larval and nymphal stages to the adult, but in the water 

 mites only three stages are noted subsequently to the egg, viz. the 

 larva, nymph and adult or prosopon, between each of which meta- 

 morphosis takes place. The eggs are usually reddish in colour and 

 laid on aquatic vegetation or stones to which they are fixed by a 

 mucilaginous covering. In the genus Hydrachna, the eggs are placed 

 in cavities pierced in the stems of aquatic plants for their reception. 

 The larval and nymphal stages are usually parasitic on aquatic 

 insects and are separated by resting stages when the creatures are 

 concealed in the axils of leaves or under stones. The adults are free 

 living. For further details, see Soar and Williamson (1925, 1927, 

 1929). 



The life cycle of the Acaridiae is similar to that of other mites, 

 passing as it does through that of egg, hexapod larva and two 

 nymphal stages before becoming adult. In some cases, however, 

 an additional heteromorphic stage is introduced into the life 

 history between the two nymphal stages. This is known as the 



