LIBELLULA. 245 



and many species of this animal are gre- 

 garious, and their immigrations in swarms are 

 well known. The butterfly and moths, as 

 you know, lay eggs which produce cater- 

 pillars, and these caterpillars, after feeding 

 upon vegetable food, spin themselves or 

 frame houses or beds, cocoons, in which 

 they are transformed into aurelias, and from 

 which they burst forth as perfect winged in- 

 sects. The libellula, or dragon fly, the most 

 voracious of the winged insect tribe, deposits 

 her eggs in such a manner, that the larvae 

 fall into the water, and, after destroying and 

 feeding upon almost all the aquatic insects 

 found in this element, and changing their 

 skins at various times, they emerge in their 

 winged form the tyrants of the insect gene- 

 rations in the air. The gnats and tipulae 

 have a similar existence. The gnat, the 

 female of which only is said by De Geer to 

 bite man, or suck human blood, in Sweden, 

 lays her egg in a kind of little boat or co- 

 coon of her own spinning. These eggs are 

 hatched on the surface of the water, and 

 produce the larvae, which undergo another 

 R 3 



