166 A BOOK OF INSECTS 



jacks or "click" beetles of the family Elateridce, when 

 surprised and thrown upon their backs, are able to leap 

 high into the air. This feat is rendered possible by a 

 "prosternal process" — a kind of dagger-like projection 

 from the front part of the thorax beneath, which fits 

 into a corresponding groove of the middle thoracic ring. 

 Before jumping, a skipjack arches its body strongly so 

 as to free the dagger-like projection from its groove, and 

 to obtain a purchase for its rapid re-insertion. In this 

 way the tip of the abdomen is made to act as a lever; 

 and when the prosternal process is shot back into its 

 groove with a sharp click, the insect is hurled through 

 the air, and nearly always comes on its legs. It has 

 sometimes been said that the beetle goes through this 

 performance in order to right itself should it chance to 

 fall upon its back ; but the fact that it usually " feigns 

 death " when it reaches the ground at the conclusion of a 

 leap suggests that the real object of the manoeuvre is to 

 escape from danger. Certain Central American skipjacks 

 have conspicuous eye-like spots upon the upper surface 

 of the thorax; and when, after their sudden jerk through 

 space, they lie motionless with legs and antenna? tucked 

 out of sight beneath the body, they have the appearance 

 of villainous-looking little reptiles — a resemblance which 

 probably serves to scare away their enemies. 



Some insects have the power of fighting in retreat. 

 This is the case with the common bombardier beetle 

 (Brachinus crepitans), which is preyed upon by larger 

 species of its own family. When one of these gives chase, 

 the bombardier ejects an acid fluid from glands situated 

 at the tip of its abdomen. This effusion immediately 

 vaporises on contact with the air, and looks like a tiny 

 puff of smoke ; while at the same time a distinct report 

 is heard, reminding one of a miniature cannon. The dis- 



