COLEOPTERA 111 



the small beetles that are seen swimming in numbers on the 

 surface of the water, the common name coming from the 

 habit of swimming rapidly in circles. The scientific name 

 for the family is also suggestive of this habit. They do 

 not exceed three-eighths of an inch in length and some 

 common forms are not more than half that long. They 

 are called " money-bugs" and "sweet-bugs" by children. 



Larger, usually, than the whirligig-beetles are the 

 Water-scavengers or Hydrophilidce. They are pointed oval 

 in shape, both ends of the body being narrowed in about 

 the same degree. On the under side of the thorax is a 

 long spine-like process that serves as a keel. They live 

 mostly under the surface of the water and fly to the 

 lights at night. One of the largest species may, in some 

 localities and at certain times, be collected by the hun- 

 dreds under a single electric light near the water. The 

 common form is more than an inch long and shining black 

 in color. 



Predaceous diving-beetles (Dytiscidce) rival the Hydro- 

 philids in size but are flatter and have the heads more 

 squarely cut off. They also lack the keel. The larger 

 species are of a dull olive-green color, marked with 

 yellow and smaller ones are black and yellow, sometimes 

 being mostly yellow. They also may be attracted to 

 lights. Their larvae are called Water-tigers. They are 

 long and slender, pointed at the rear end, and have power- 

 ful jaws. They are, without exception, the fiercest ani- 

 mals that live in the water. The larva of the largest 

 common diver is three inches in length. 



68. Scavenger Beetles. Several families of beetles, 

 not typically scavengers, include species that feed on re- 

 fuse and carrion. In two families, however, almost all 

 forms feed on decaying organic matter. These are the 



