144 INSECTS DIPTERA DIAGRAM 6. 



The Fly. There are a great many different species of flies, 

 some of which have a fine blue or green metallic colour. In the 

 larva state the fly is called a maggot. Anglers use them to bait 

 their hooks. The blue flesh-fly lays its eggs on meat which is 

 beginning to decompose. The eggs are white, rather large, and 

 form in small clusters. The maggots which proceed from them 

 feed on the putrefying meat. When the time has come for them 

 to undergo their metamorphosis, they hide in dark and dry 

 places. When they have found a place that suits them, they 

 shrink up, turn brown, and thus become chrysalides without 

 making a cocoon, or changing their skin. At the end of about 

 eleven days, the fly emerges from the chrysalis. 



The old skin of the larva splits at one end, as if it could not 

 contain the animal within it. The fly, when ready to emerge, 

 swells its head, which makes the chrysalis split ; it swells itself 

 again to get rid of the covering which surrounds it ; and at last 

 it stands on its legs ; but it is pale in colour, its wings are soft, 

 and it cannot fly, and remains quiet in one place. But in a few 

 minutes its wings have dried, its skin has become dark, and it flies 

 away. 



The (Estrus is a fly the larva of which has very singular habits. 



The fly lays its eggs on living 

 animals, horses, oxen, or 

 sheep. As soon as the larvse 

 are hatched, they bury them- 

 selves under the skin, where 

 they remain, and sometimes 

 (Estrus. Lava of (Estrus. form a small tumour in which 



the larvre are found when they are opened ; they only leave it 

 when they are about to go into the pupa state, when they fall on 

 the ground, and there undergo their last metamorphosis. 



But some cestri lay their eggs on the fore legs of the horse, 

 where he can reach them with his tongue. When he begins to 

 feel a little pain there, he licks the spot, and swallows the young 

 larvae. Their strong outer skin cannot be digested by the 



