284? INDIRECT BENEFITS DERIVED FROM INSECTS. 



men, who call them manna : and when their season is 

 come, they say "the manua begins to appear, the manna 

 fell abundantly such a night;" alluding, by this expres- 

 sion, either to the astonishing quantity of food which the 

 Ephemerae afford the fish, or to the large quantity of 

 fish which they then take. 



Reaumur first observed these insects in the year 1738, 

 when they did not begin to show themselves in numbers 

 till the 18th of August. On the 19th, having received 

 notice from his fisherman that the flies had appeared, he 

 got into his boat about three hours before sun-set, and 

 detached from the banks of the river several masses of 

 earth filled with pupae, which he put into a large tub full 

 of water. This tub, after staying in the boat till about 

 eight o'clock, without seeing any remarkable number of 

 the flies, and being threatened with a storm, he caused 

 to be landed and placed in his garden, at the foot of 

 which ran the Marne. Before the people had landed it, 

 an astonishing number of Ephemeras emerged from it. 

 Every piece of earth that was above the surface of the 

 water was covered by them, some beginning to quit their 

 slough, others prepared to fly, and others already on the 

 wing; and every where under the water they were to be 

 seen in a greater or less degree of forwardness. The 

 storm coming on, he was obliged to quit the amusing 

 scene ; but when the rain ceased to fall he returned to it. 

 As soon as the cloth with which he had ordered the tub 

 to be covered was removed, the number of flies appeared 

 to be greatly augmented, and kept continually increasing : 

 many flew away, but more were drowned. Those al- 

 ready tiansformed, and continually transforming, would 

 have been sufficient of themselves to have made the tub 



