244 INSECTS AND MAN 



that it is highly improbable that they will walk from one 

 cheese to another. When no more food is at hand, the 

 young mites and the old ones die off, and considerately 

 leave the field clear for the more vigorous, middle-aged 

 individuals. The survivors completely change their form 

 by acquiring a hard, brown, protective covering, into which 

 their legs can be drawn, and, at the same time, their exist- 

 ence, without food, can be almost indefinitely prolonged. 

 This is known as the hypopus stage. As everything comes 

 to him who waits, sooner or later a mouse or a house fly 

 or perhaps a cockroach comes along in quest of food, the 

 hypopus shoots out its legs and eagerly seizes some con- 

 venient hair, to which it clings, till it is carried to a spot 

 where suitable food is at hand, then, relaxing its hold, it 

 throws off its horny coat and begins life afresh. 



Another inhabitant of cheese and harn is the " skipper," 

 Piophila casei (fig. 66). It is, perhaps, not quite so well 

 known as the mites, though more repulsive when encoun- 

 tered, because its greater size makes it more obvious, and 

 the old dictum about " What the eye doesn't see, etc.," 

 applies just as forcibly in household entomology as in other 

 directions. Like the cheese mites, the cheese skipper is 

 cosmopolitan. It derives its name from the wonderful 

 leaping powers of the maggot or larva, which, although 

 only one-fifth of an inch long, can jump to a height of 

 three to four inches, by bringing the two ends of its body 

 together and then suddenly releasing them like a spring. 

 The " skipper " is the larval form of a small, glistening, 

 black, two-winged fly, which lays its eggs in the outer, 

 fatty parts of hams or in cheeses, preferably the best. 

 Each female lays about thirty slender, oblong, and slightly 

 curved white eggs, either in compact clusters of five to 

 fifteen, or, occasionally, they are scattered singly. In thirty- 

 six hours the eggs hatch into small white, cylindrical, 

 legless maggots or skippers, which taper gradually to the 

 anterior or head end, whilst the posterior truncate end is 



