192 INDIRECT BENEFITS DERIVED FROM INSECTS. 



roach, &c., will hold it by the legs so that it cannot move, till some of 

 them get upon it and despatch it, and then, with incredible labor, carry- 

 it up to their nest. Madame Merian, in her account of the periodical 

 ants mentioned to you before, and which is confirmed by Azara^, notices 

 their clearing the houses of cock-roaches and similar animals ; and Myr- 

 mica omnivora is very useful in Ceylon in destroying the former insect, 

 the larger ant, and the white ant.^ 



You are not perhaps accustomed to regard wasps and hornets as of 

 any use to us ; but they certainly destroy an infinite number of flies and 

 other annoying insects. The year 1811 was remarkable for the small 

 number of wasps, though many females appeared in the spring, scarcely 

 any neuters being to be seen in the autumn^ ; and probably in consequence 

 of this circumstance, flies in many places were so extremely numerous as 

 to be quite a nuisance. Reaumur has observed that in France, the 

 butchers are very glad to have wasps attend their stalls, for the sake of 

 their services in driving away the flesh-fly ; and, if we may believe the 

 author of Hector St. John's American Letters, the farmers in some parts 

 of the United States are so well aware of their utility in this respect, as 

 to suspend in their sitting-rooms a hornet's nest, the occupants of which 

 prey upon the flies without molesting the family. 



There are other devourers of insects in their perfect state, the manners 

 and food of whose larvae we are unacquainted with. St. Pierre speaks 

 of a lady-bird, but it probably belonged to some other genus, of a fine 

 violet color, with a head like a ruby, which he saw carry off a butterfly.^ 

 Linne informs us that Cler us formicarius devours Anobium pertinax. A 

 fly related to Panorpa communis appears created to instil terror into the 

 pitiless hearts of the tyrants of our lakes and pools — the all-devouring 

 Lihellulina/' The Asili also, which are always upon the chase, seize 

 insects with their anterior legs and suck them with their haustellum. The 

 cognate genus Dioctria, particularly D. celandica, prey upon Hymenoptera, 

 by some unknown means, instantaneously killing the insect they seize. 

 Many species also of Empis, whose haustellum resembles the beak of a 

 bird, carry off in it Tipularia and other small Diptera ; and, what is 

 remarkable, you can seldom take these insects in coitu, but the female has 

 a gnat, some fly, or sometimes a beetle, in her mouth. Can this be to 

 deposit her eggs in, as soon as they are impregnated by the male ? or is 

 it designed for the nuptial feast ? Even Scatophaga stercoraria and 

 scybalaria, and probably many others of the same tribe, feed upon small 

 flies, though their proboscis does not seem so well adapted for animal as 

 for vegetable food. 



The most unrelenting devourers of insects appear to be those belonging 

 to my fourth division, which attack them under every form. These begin 

 the work of destruction when they are larvse, and continue it during the 

 whole of their existence. The earwig that haunts every close place in 

 our gardens, and defiles whatever it enters, probably in some degree makes 

 up for its ravages by diminishing the number of other insects. The 

 cowardly and cruel Mantis, which runs away from an ant, will destroy in 



* Voyages, i. 185. * Percival's Ceylon, 307. 



' Mr. Knight made the same observation in 1806, and supposes the scarcity of neuters 

 arose from the want of males to impregnate the females. Philos. Trans. 1807, p. 243. 



* St. Pierre, Voy. 72. « Lesser, L. i. 263. note. 



