282 



HOUSEHOLD INSECTS 



from the eggs have only six legs, but after molting they 

 obtain two more. The young mites may gradually grow, 

 by shedding their skins, into the adult forms, or they may 

 pass through a curious stage, known as the hypopus 

 (Fig. 92). The hypopus is very different in every way 

 from the young mite from which it developed. The body 

 of the hypopus is hard and chitinous and its legs are very 



short and inefficient for 

 walking. The body on the 

 ventral side near the tip 

 is, however, provided with 

 several sucking disks that 

 serve a very useful pur- 

 pose when the opportunity 

 is presented. There is no 

 mouth opening and there 

 are no distinct mouth- 

 parts. Evidently the crea- 

 ture does not take food in 

 this stage. In fact, the 

 hypopus is a remarkable 



FIG. 92. Hypopus of cheese mite, ,"* J j j t 11 



much enlarged. body and wonderfully 



adapted to a peculiar 



situation. The hard covering of the hypopus protects 

 it from injury and from the influence of fluctuating 

 temperatures, humidity and other influences. In this 

 stage the mites can exist for long periods without food. 

 When favorable conditions return, the hypopus will molt, 

 when, behold ! it has changed to a young mite again which 

 feeds normally and develops to an adult in the regular 

 way. Just what influences induce a young mite to trans- 

 form into a hypopus is not known. It is evidently not 



