196 



MITES AND TICKS 



parthenogenetic, and hatches into a six-legged larva. This passes 

 through from one to three nymphal forms before becoming adult, 

 each stage in the life cycle being preceded by a resting period. In 

 most mites the larvae, except for the absence of genital openings 

 and the posterior pair of legs, somewhat resemble adults. In some 

 Prostigmata, however, they are quite different and metamorphose 

 into a nymph which is more like the adult in form. In the account 

 given below a few typical examples of life histories will be given. 



Larva 



Nymph 



Adult 



Egg 



Fig. 40. Stages in the development of an Oribatid mite (Pelops 

 sp.): 1. egg, 2. larva, 3. nymph, 4. adult. (After Michael, 1884.) 



The life history and sensory behaviour of the Mesostigmatid 

 snake mite Ophionyssus natricis has recently been investigated by 

 Camin (1953) who found that development of the eggs takes from 

 28 to 98 hours; larvae 18 to 47 hours, protonymphs 3 to 14 days, 

 deutonymphs 13 to 26 hours and adults 10 to 32 days within the 

 range of temperatures 20° to 30° C, commonly occurring in snake 

 cages in zoos. The adult female mite, after completing engorge- 

 ment, crawls out from under the scale of the host, drops from the 

 snake's body and wanders about until it finds some dark moist 

 crevice where oviposition takes place. The emerging larvae remain 

 in the moist region where there is little risk of desiccation and the 

 protonymphs stay there too until their integument becomes 

 sclerotised and the danger of death from water-loss is lessened. 

 Then they wander at random until they come upon a suitable host, 

 become concealed under a scale and commence feeding. If, on the 



