Sarcoptiformes 333 



thermore, many eat dead and decaying insects, the caloglyphids being the 

 most notable example. Apart from a few species of the genus Thyreopha- 

 giis, which live on oyster-shell scale and kindred insects, none of the family 

 appears to be either a predator or a parasite. As yet no fossil records have 

 been found of either the Acaridae or their immediate progenitors, but this 

 is not to be wondered at, as they are extremely small creatures, which do 

 not lend themselves to easy fossilization.^ 



The life cycle of the mite may be summarized briefly as follows, 

 Rhizoglyphus echinopus (Fumouze and Robin) being used as an ex- 

 ample. Garman 1937 found that at a room temperature of 60°-75° F. 

 (68° average) the mite went through its life cycle in seventeen to 

 twenty-seven days; and that at 70°-80° F. its life cycle was completed 

 in nine to thirteen days. The mite becomes torpid at 55°-50° in the 

 lower temperature range and at about 95° in the upper extreme. The 

 mite needs a rather high humidity. Garman Hsts the stages as follows 

 (between each stage, except egg and larva, the mite becomes quies- 

 cent). 



A. Cycle in which the hypopial stage (second nymph) is omitted 

 Egg — larva — first nymph — third nymph 



adult female 

 normal male 

 heteromorphic male 



B. Cycle with hypopial stage (second nymph) 



Egg — larva — first nymph — hypopus — third nymph 

 adult female 

 normal male 

 heteromorphic male 



Many of the Acaridae have a hypopial or "wandernymph" stage in 

 which the mite changes into a small creature with suckers or claspers 

 for grasping insects for dispersal, and at times they have been mistaken 

 for parasites. Apparently the mites can withstand dryness best in this 

 stage. The hypopus of one species ha^ even been taken from the gill 

 chambers of a moUusk and another from the gonads of a millipede. 

 Whereas the length of the hypopal stage is from five to thirteen days, 

 the other stages are from three to eight days or less. The hypopi then 

 develop into nymphs which may produce any type of adult. Michael 

 1901 found hypopi of various acarids produced under several condi- 

 tions and could describe no reason for their development. Garman 



1 FromNesbitt 1945. 



