FIELD BOOK OF PONDS AND STREAMS 





Fig. 217. — Eggs oiDonacia glued to the underside 

 cf a lily pad around the hole which has been cut by 

 the beetle. 



conspicuous white egg-clusters are easy to find upon most 

 lily pads all through the summer and early fall. 



In about ten days the eggs hatch and the larvae begin a re- 

 markable existence in which, though living two feet or more 

 below the surface, they constantly breathe air. Dropping 

 down through the open water these larvae seek the under- 

 ground stems of the plant on which their own species of 

 Dofiacia has lived for generations. When the stems of aquatic 

 plants are broken beneath the water a flood of air bubbles 

 comes pouring to the surface from the air spaces within them. 

 The little Donacia larvae rasp their spines against such stems, 

 break through the walls of the air spaces, then push their 

 heads into the holes they have made (Fig. 218). Thus, the 

 larva taps the air suppl}^ of the plant and its head and thorax 

 are surrounded by a layer of continually escaping air. Alac- 

 Gillivray and others found stems with dozens of little Donacia 

 larvae hanging to them feeding upon the plant tissues, and all 

 breathing air, though they were three or four feet below the 

 surface of the water. 



When fullgrown the larva spins a water-tight cocoon pro- 

 visioned with air from the air spaces of the plant. When the 

 adult emerges from the cocoon at the end of pupation, some 

 of this air catches in the silken hairs on the ventral side of 



280 



