DIPTEEA. 37 



every situation ; some inhabiting woods, plains, fields, or banks 

 of rivers ; others preferring our houses. They each take their 

 share of vegetation, preferring either the flowers, the leaves, 

 or the stems of the trees of our woods, our gardens, or our planta- 

 tions. Their food varies very much ; and the formation of the 

 sucker is regulated by it. Some imbibe blood, others live on the 

 secretions of animals. Their chief nourishment, however, consists 

 of the juices of flowers, on whose brilliant corollas the Diptera 

 abound, either plundering from every species indiscriminately, 

 or attaching themselves to some particular kind. They dis- 

 play the most wonderful instinct in their maternal care, and 

 employ the most varied and ingenious precautions to preserve 

 their progeny. 



The Diptera, besides their variety and the number of their 

 species, are remarkable on account of their profusion. The myriads 

 of flies which rise from our meadows, which fly in crowds around 

 our plants, and around every organised substance from which 

 life has departed, some of which even infest living animals, are 

 Diptera. 



The profusion with which they are distributed over the face 

 of the globe, causes them to fulfil two important duties in the 

 economy of nature. On the one hand, they furnish to insecti- 

 vorous birds an inexhaustible supply of food ; on the other, they 

 contribute to the removal of all decaying animal and vegetable sub- 

 stances, and thus serve to purify the air which we breathe. Their 

 fecundity, the rapidity with which one generation succeeds 

 another, and their great voracity, added to the extraordinary quick- 

 ness of their reproduction, are such that Linnaeus tells us that 

 three flies with the generations which spring from them could eat 

 up a dead horse as quickly as a lion could. 



These Diptera, which are worthy of so much attention, and de- 

 serve so much study with regard to the part they play in the general 

 economy of nature, are an object of fear and repulsion when one 

 considers their relations to us and other animals. Gnats and 

 mosquitoes suck our blood ; the gad-fly and the asilus attack our 

 cattle. The order Diptera is composed of a great number of 

 families, and these families are again divided into tribes, which 

 themselves comprise several genera. We shall only speak of 



