34 THE INSECT WORLD. 



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 display 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 insectivorous birds an 

 inexhaustible supply of food ; on the other, they contribute to the 

 removal of all decaying animal and vegetable substances, 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 quickness 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 

 deserve 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 species of Asilus 

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

 of families, which are again divided into tribes, each comprising 

 several genera. We shall only notice the more remarkable genera of 

 Diptera. 



M. Macquart, the learned author off "L'Histoire Naturelle des 

 Dipteres,"* divides this great class of insects into two principal groups. 

 In one of these groups, the antennae are formed of at least six joints, 

 and the palpi of four or five : these are called Nemocera. In the 

 other, the antennae consists only of three joints, and the palpi of one 

 or two : these are the Brachycera. 



The Nemocera may generally be distinguished from the other 

 Diptera, independently of the difference in the antennae and palpi, by 



* " Suites k Buffon." 2 vols. 8vo. 



