438 THE NATURAL HISTORY 



that troublesome fly that in sunny weather is per- 

 petually swarming round the heads of horses and 

 cattle. Every one who has taken a ride or a drive in 

 summer must have noticed this phenomenon, and been 

 struck with astonishment at the wonderful strength of 

 wing and endurance which enable these insects to 

 keep pace in this way with a trotting horse. 



The well known scavengers, Sarcophaga carnaria, 

 the Flesh fly, Musca Ccesar, the Bluebottle fly, and 

 Musca vomitoria, the Meat fly, belong to this division. 

 The first of these performs its task with such amazing 

 expedition that three of them, according to Linnaeus, 

 would devour the carcase of a dead horse as quickly 

 as would a lion. Taken in its obviously proper sense, 

 as referring to the larvae of the flies, this statement, 

 which has been a thousand times quoted in entomo- 

 logical works, is probably no very great exaggeration, 

 and it is quite certain that the work performed by 

 them, under favourable conditions, would astonish any 

 one who, for the first time, made himself acquainted 

 with their proceedings by personal observation. In 

 the first place, the delay involved in the laying and 

 hatching of eggs would be avoided, and sixty thousand 

 living and unmistakably Voracious "maggots" would 

 in a very short time be placed in a position to do 

 justice to their fare. These would devour so much, 

 and grow so quickly, that in the short space of twenty- 

 four hours they would be two hundred times heavier 

 than they were at their birth, and, assuming that this 

 rate of rapid development continued four days longer, 

 by which time they would be full grown, they would 

 have increased in bulk a thousand-fold before they 

 had ceased feeding. We once witnessed, in a not very 

 distant private collection of Exotics, the result of 

 what to us appeared a curious error of instinct in one 

 of these flies, deceived by the carrion-scented blossoms 

 of a species of Stapelia, which was there growing 

 luxuriantly, it had deposited so many of its larvae in 



