154 PIIRYGANL.E. 



are vulgarly called green flies and yellow flies, from 

 the colours of their bodies, and also willow flies, alder 

 flies, or other names, according to the trees that may 

 be most prevalent on the banks of the rivers, as they 

 usually deposit their young on the leaves of trees. 

 The eggs are attached to those parts of the tree that 

 hang over the stream, the mother glueing them on 

 with a viscid juice that nature has supplied her with 

 for the purpose. The eggs remain there till they are 

 hatched, and produce larvce, which are long, with the 

 body divided into rings, and having six feet. When 

 those larv<z fall into the water they would instantly be 

 devoured by water beetles, by fish, and by the larvce of 

 other insects, such as those of the dragon-fly and the 

 dytiscus beetle, were it not that they instantly build a 

 house or case for themselves. These houses are formed 

 of various substances, as grains of sand, small shells, 

 bits of vegetable matter, cemented together by a glue 

 which the larva produces. One species makes choice 

 of lemna or duck-meat, the little green plant which 

 covers the surface of ponds and other stagnated waters 

 in the summer. The leaves of the duck-meat are 

 naturally round, and therefore not very well adapted 

 for being united into a solid fabric without a great waste 

 of materials , but the larva cuts them into perfect 

 squares, and puts them together so neatly, that its 

 house seems to be covered with a delicately chequered 

 green riband wrapped spirally round it. This case 

 connects them entirely, but they can at pleasure pro- 

 trude the head for the purpose of feeding, which they 

 do indiscriminately upon vegetable and animal food. 

 These larvae are well known to anglers, who give them 



