138 



THE STUDY OF INSECTS 



quite closely in size and color, but which may be distinguished by the 

 comb-like form of the tarsal claws; this is Lebia grandis (Fig. 228). 

 It has been reported more often than 

 any other insect as destroying the Col- 

 orado potato-beetle. 



What is perhaps the most common 

 type of ground-beetle is illustrated by 

 Harpalus caliginosus, which is represented 

 natural size in Figure 229. It is of a 

 pitchy black color, and is one of the most 

 common of our larger species. There are 

 one hundred and thirty-six described 

 species of Harpalus in this country. Most 

 of them are smaller than this one, are 

 flattened, and have the prothorax nearly 

 square. 



The most common of all ground-bee- 

 tles, in the Northeastern States at least, 

 is Pcecilus lucublandus. In this species 

 (Fig. 230) the narrow, flat margin on each 

 side of the prothorax is widened near the hind angle of this segment. 



Fig. 22g. 



Fig. 228. — Lebia gran- 

 dis, natural size and en- 

 larged 



Fig. 230. 



Family Dytiscid^ 



The Predacious Diving-beetles 



If one will approach quietly a pool of standing water, there may be 

 seen oval, flattened beetles hanging head downward, with the tip of the 

 abdomen at the surface of the water. Such beetles belong to this family. 

 The predacious diving-beetles are usually brownish black and shining, 

 but are often marked indefinitely with dull yellow. They can be dis- 

 tinguished from the water scavenger-beetles, which they resemble in 

 general appearance, by the thread-like form of the antenna?. The hind 

 legs are the longest and are fitted for swimming, being flattened and 

 fringed with hair. The middle and the hind 

 pair of legs are widely separated. In the 

 males of certain genera the first three seg- 

 ments of the fore tarsi are dilated and form 

 a circular disk, upon the under side of which 

 are little cup-like suckers (Fig. 231). The 

 females of some species exhibit an interesting 

 dimorphism in that some of the individuals 

 have the elytra furnished with a number of deep furrows (Fig. 232), 

 while others of the same species have them smooth. 



The diving-beetles abound in our streams and ponds, but they are 

 more often found in standing water than in streams. When at rest they 

 float in an inclined position, head downward, with the tip of the hind end 

 of the body projecting from the water. The spiracles open on the dorsal 

 side of the abdomen beneath the elytra. By lifting the elytra slightly a 

 reservoir is formed for air, which the beetle can breathe as it swims 

 through the water. When the air becomes impure the beetle rises to the 

 surface, forces it out, and takes a fresh supply. 



Fig. 232. 



