480 



AN INTRODUCTION TO ENTOMOLOGY 



Fig. 560. 



is secreted a bad-smelling fluid, which is used 

 as a means of defence. These beetles spurt this 

 fluid out onto their enemies when attacked. 

 But in the case of the bombardier-beetles this 

 fluid changes to a gas, which looks like smoke 

 as soon as it comes in contact with the air, and 

 is ejected with a sound like that of a tiny pop- 

 gun. When some larger insect tries to capture 

 one of these insect-soldiers, and gets very 

 near it, the latter fires its little gun into the face 

 of its enemy. The noise astonishes the pursuer, 

 and the smoke blinds him. By the time he 

 has recovered from his amazement, the little bombardier is at a safe 

 distance. These beetles have quite a store of ammunition; for we 

 have often had one pop at us four or five times in succession, while we 

 were taking it prisoner. The bombardier-beetles belong to the genus 

 Brachinus, of which we have in this country twenty-seven species. 

 They are very similar in appearance; the head, prothorax, and legs 

 are reddish yellow, and the wing-covers are dark blue, blackish, or 

 greenish blue (Fig. 561). 



There is a common beetle which resembles the bom- 

 bardier-beetles 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. 562). It has been 

 reported more often than any other insect as destroying 

 the Colorado potato-beetle. 



Galerlta jdnns is still another species that bears some 

 resemblance to the bombardier-beetles. But it is much 

 larger, measuring 16 mm. in length, and has only the prothorax and 

 legs reddish yellow, the head being black ; the prothorax is only about 

 half as wide as the wing-covers. 



What is perhaps the most com- 

 mon type of ground -beetle is illus- 

 trated by Hdrpalus caliginosus, 

 which is represented natural size 

 in Figure 563. 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 de- 

 scribed species of Harpalus in this 

 country. Most of them are smaller 

 than this one, are flattened, and have 

 the prothorax nearly square. 



The beetles of the genus, Diccelus 

 are quite common ; and some of the 

 larger species resemble Harpalus 

 caliginosus quite closely. They can 

 be distinguished by a prominent keel- 

 shaped ridge which extends back upon each wing- 

 cover from near the corner of the prothorax. 



Fig. 561. 



Fig. 563. 



Fig. 562. — Lebia 

 grandis, natu- 

 ral size and 

 enlarged. 



Fig. 564. 



