EIGHTH DAY.] LIBELLULA. 209 



and many species of this animal are gregarious, and 

 their emigrations in swarms are well known. The 

 butterfly and moths, as you know, lay eggs which pro- 

 duce caterpillars ; 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 insects. 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 generations in the air. The gnats and tipulse 

 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 cocoon of her own spinning. These eggs 

 are hatched on the surface of the water, and produce 

 the larvae, which undergo another change into peculiar 

 nymphse, that still retain the power of swimming and 

 moving, from which the perfect insect is produced 

 during the summer heat. The flies, which I 

 mentioned to you in a former conversation, under 

 the name of the grannom, or green tail, (see fig. 2,) 

 are of the class pAryganea, which includes all those 



