78 OUR INSECT FRIENDS AND FOES 



the pond during the afternoon and evening, and 

 flies away to another. It seems highly probable 

 that these migrations from one pond to another 

 have helped to spread the Canadian Pond Weed 

 (Elodea canadensis\ which has become naturalized 

 in England, as the Beetles have been observed 

 coming out of ponds where the plant has estab- 

 lished itself, with fragments of its stem attached 

 to them. This plant, which is a native of 

 North America, was first noticed growing wild 

 in England in 1842, and again in 1847, since 

 when it has spread to nearly every lake and 

 river throughout Britain. So rapid and prolific 

 is it in its growth, that many ponds have been 

 quite choked up by it, and numerous shallow 

 streams seriously affected. The stems of this 

 plant are very brittle, and as the smallest frag- 

 ment of a stem, if allowed to remain in the water, 

 will develop one or two branches which in turn 

 will throw out new growths, a luxuriant mass 

 is formed in an incredibly short time. All 

 kinds of water-fowl are fond of feeding upon 

 it, and like the Dytiscus Beetle are very apt 

 to bear fragments away with them, so that they 

 also havemndoubtedly helped in the spreading of 

 this plant from one pond or stream to another 

 throughout England. 



The Great Water Beetle (Hydrophilus piceus) 

 attains a length of about two inches, and with the 

 exception of the Stag-beetle, it is the largest of 

 our British Coleoptera. In the adult stage of 

 its life it is a very handsome Beetle, and feeds 

 almost exclusively on vegetable matter, only very 

 occasionally preying upon the smaller inhabitants 



