416 RAVAGES OF INSECTS. 



multiplication of the cheese-fly is checked by some insect, 

 whose history, so far as we are aware, is not yet known. 

 Swammerdam found many of the maggots with other larvae 

 in their bodies ; but he did not trace their transformations. 

 If they were the larv£e of an ichneumon, it must be ex- 

 ceedingly minute. 



It must have attracted the attention of the most in- 

 curious, to see, during the summer, swarms of flies crowd- 

 ing about the droppings of the cattle, so as almost to con- 

 ceal the nuisance, and presenting instead a display of their 

 shining corslets and twinkling wings. The object of all 

 this busy bustle is to deposit their eggs where their progeny 

 may find abundant food ; and the final cause is obviously 

 both to remove the nuisance, and to provide abundant food 

 for bii'ds and other animals, which prey upon flies or their 

 larvge. The same remarks apply with no less force to the 

 blow-flies which deposit their eggs, and in some cases their 

 young, upon carcases. The common house-fly (^Musca 

 domestica) belongs to the first division, the natural food of 

 its larvae being horse-dung ; consequently it is always most 

 abundant in houses in the vicinity of stables, cucumber 

 beds, &c., to which, when its numbers become annoying, 

 attention should be primarily directed, rather than having 

 recourse to fly-waters. 



Another common insect (^Bihio liortulanus, Meiq-ets") 

 lives in the larva state in cesspools, along with rat-tailed 

 larvae, &c. The maggot of the bibio is very peculiar in 

 form. They are hatched from eggs with shells as hard as 

 Paris plaster, deposited on the adjacent walls, and fre- 

 quently upon the pupa-case which the mother has pre- 

 viously quitted. Like the lai-^^as of the crane-flies above 

 described, this one moves itself chiefly by means of its 

 mandibles, and therefore it can make no progress on a 

 piece of smooth glass. Its skin, it may be remarked, is 

 so exceedingly hard and tough, that it is no easy matter 

 to kill it,* We have introduced this insect here, how- 



* Swanmierdam, x. 212, 



