82 DKAGOX FLIES VS. IMOSQUITOES. 



of which are knowu under various names, as House fly 

 (Musoa domestica), Bhiebottle fly, Green fly (Musca cse- 

 sar), Meat fly (jNIusea voniitoria), etc., and which are 

 the most common species which infest our houses, and, 

 attracted by the odors and refuse of the kitchen, out- 

 houses, stables, and poultry and cattle yards, fearlessly 

 invade the privacy of our dwellings and rudely trespass 

 upon our persons and food. On the other hand many 

 of the Muscidee, as Tachina, are parasitic upon caterpil- 

 lars and coleopterous larvae, and so beneficial are they 

 in this respect that, so far as my experience goes, it is not 

 extravagant to say that without their aid there would 

 be no crops to harvest nor forests for timber. A single 

 female Tachina will destroy an entire brood of one hun- 

 dred Datana larvae, each one of which is from twenty to 

 thirty times heavier than herself — a fact which I myself 

 have witnessed. Out of three hundred larvae of Danaus 

 archippus collected this summer, only about one hundred 

 w^ere free from Tachina, and these escaped very largely by 

 being taken during the first moult. Again, there are Dlp- 

 tem (Asilidae) which, though not parasitic as the Tachina, 

 are direct destroyers of other insects and are of equal 

 value Avith dragon flies in this respect. The largest and 

 most voracious species of this family are found in the 

 fields adjoining our dwellings, where they are distributed 

 in great numbers, every step arousing one or more. Bee 

 and butterfly alike are palatable morsels to them, and, as 

 they never rise from the surface of the ground, they catch 

 many insects which the dragon fly is unable or unwilling 

 to take. Besides the Muscidae there are many families of 

 Diptera (CEstridae — bot flies, etc.) which are very annoy- 

 ing to man and the lower animals, but, as the dragon fly 



