244 



INTRODUCTION TO ZOOLOGY 



captivity, and will live for several years if well fed. Its 

 natural food consists of tadpoles and soft-bodied larvae and 

 even small fish, but it can be fed on " gentles," l which 

 it will devour eagerly. In spite of its carnivorous habits 

 and strong mandibles, the beetle may be handled without 

 any worse consequences than a possible prick from the two 

 little sharp spines that are present on the under side of the 

 body just between the last pair of legs, or a discharge of 

 a bad -smelling fluid, either from just behind the head or, 

 sometimes, from the end of the body. 



The sexes are very distinct. In both, the body 



is about *i incnes lon g an(i of an olive-brown 

 colour, with a light -brown border running all 

 round the thorax and down the outer margin of the elytra ; 

 but whilst in the male the surface of 

 the elytra is nearly always smooth, in 

 the female it is usually deeply furrowed 

 from the base for half its length. This 

 distinction, however, is not quite in- 

 variable, and a safer guide is the curious 

 disc which is always present on the 

 front legs of the male only (Fig. 169, 

 d) ; it is formed from the much-enlarged 

 first three segments of the five-segmented 

 foot or tarsus. When the under sur- 

 face of this disc is examined, each 

 segment is found to be beset with a 

 number of small stalked suckers with 

 two much larger ones on the first tarsal 

 joint (Fig. 170). The terminal portion 

 of each of these suckers, small or large, 



is slightly concave, and strengthened 

 FIG. 170. Tarsus from . . & ,/,. . . _ , 



the fore-leg of a male Wltn radiating ribs ; when it is firmly 

 Dyticus. pressed on any surface, considerable 



Under-side, showing the disc SUCtion results, though, according to 



first jy[ r Lownes's account, 2 this seems to 

 be owing not merely to adhesion due 

 to atmospheric pressure on the upper 

 surface of the sucker, but also to an adhesive liquid that is 

 given out by it. These adhesive discs seem to be used by 

 1 See p. 331. 2 Month. Micr. Journ. vol. v., 1871, p. 267. 



formed from the 

 three segments of 

 tarsus. 



the 



