II FLIES WITH AQUATIC LARV^ 217 



attributes this belief to the swarming of the bee- 

 like Bot-fly of the horse (Gastrophilus equi) about 

 horses. The belief would be strengthened by the 

 occasional productions of the wasp-like Helophilus 

 (a close relative of Eristalis) from carcasses of the 

 horse, though any other dead body would do as 

 well. 



It may be asked whether the ancient husbandmen 

 were not acute enough to find out that their Bees, 

 formed according to prescription, laid no honey ; and 

 further, why no Insects, likely to be mistaken for 

 Bees, are seen to issue from carcasses in our own 

 time and country. The experimenters of old were, 

 we must suppose, satisfied to let their swarms of arti- 

 ficially produced Bees fly abroad. It was enough in 

 their eyes to have saved the race from extermination. 

 Bee-keepers, even in the Augustan age, no doubt 

 knew better ways than this of getting swarms into 

 their hives, and the supposed generation of Bees from 

 carcasses was probably a belief rather than a method 

 likely to be tried by practical men. The answer to 

 the second question may be given in Osten Sacken's 

 own words : — " The larva of Eristalis, being aquatic, 

 requires a pool of stagnant water containing putrescent 

 organic matter. A carcass, left in the open air, is at 

 once attacked by the ordinary carcass-loving flies, 

 Liicilia, Calliphora., &c. During the second stag€ of 

 putrescence a pool of corrupt liquid is formed about 

 the carcass, and then is the time for Eristalis to 

 appear. In the present age of sanitary police a 

 carcass would never reach this stage." But in Lap- 

 land Zetterstcdt, as quoted by Osten Sacken, found 



