COLOUR OF THE WATER BEETLE. 49 



being directed to the end of the abdomen. What 

 may be the object of this curious appendage is not 

 easy to say ; certain, however, it is, that it can be 

 used as a weapon on some occasions. 



When, for example, an unpractised entomologist 

 catches one of these Beetles in his hand, and has 

 taken care to keep his fingers out of the way of its 

 jaws, he finds himself suddenly and smartly wounded 

 as the Beetle struggles to regain its liberty. The fact 

 is, the insect, led by some strange and unaccountable 

 instinct, always retrogrades when seized in the hand, 

 and so inflicts a rather unpleasant wound with the 

 ends of this appendage. Whether or not it knows of 

 the presence of the weapon, and the use to which it 

 is put, is of course impossible to say ; but that the 

 insect can use its forked dagger as well as if it were 

 thoroughly acquainted with it, any of my readers can 

 easily test for himself by going to the nearest pond 

 and catching a Dyticus. Other Water Beetles possess 

 the forked appendage ; but it takes different shapes in 

 different species, and is exceedingly useful to entomo- 

 logists, by enabling them to decide upon the species 

 when other marks fail them. 



As the two sexes are so dissimilar in appearance, 

 it will be necessary to describe them separately. The 

 colour of the male Beetle is dark olive, with the 

 margins of the elytra marked with a yellowish streak, 

 narrow towards the apex, and widening considerably 

 towards and on the shoulders. It is in consequence 

 of this streak that the Beetle has received the specific 

 name of marginalis. The elytra are very smooth, 

 with the exception of three rows of punctures on the 



E 



