BRITISH INSECTS 



species whose larvas live in filthy water, on excrement, 

 and other insanitary places. There are others {Volu- 

 cella) which prefer taking up their abode in the nests 

 of humble-bees and wasps, and others again (Merodon) 

 which feed upon narcissus bulbs, and perpetrate con- 

 siderable damage. There are a number of dipterous 

 flies belonging to the Family Tachinidce, many of the 

 larvae of which are, like the very large family of Ichneu- 

 mons, parasitic in caterpillars. There is, however, this 

 difference that whereas the female Ichneumon Fly 

 pierces the skin of the caterpillar, and at once deposits 

 her eggs inside the host, the Tachinidce have no ovipositor 

 with which to make the puncture, and thus deposit 

 their eggs on the outside. The larva, on hatching, 

 however, soon eats through the skin, and works its way 

 to the interior upon which it feeds. 



Of the House Fly {Musca domestica), and Blow Fly 

 {Musca corvina) — both of which belong to the Family 

 Muscidce — it is only necessary to say that, whereas they 

 and their numerous congeners act as scavengers and 

 sanitary-agents, there is another side to the picture as, 

 feeding very often in distasteful places and then visiting 

 our own food-stuffs, they are not altogether friends 

 worthy of encouragement. They do some good, they 

 also perpetrate much harm. Decaying matter soon 

 attracts females to the spot, eggs are laid, grubs soon 

 hatch, and thrive upon the filth that is provided. The 

 general appearance of these familiar creatures does not 

 call for mention. 

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