The Great Water -Beetle, 423 



that he was unable to find any remains in the intestinal canal, 

 upon his dissecting the beetle shortly afterwards. The 

 voracious habits of the larva of Dyticus are as great as they 

 are in the perfect insect ; but owing* to the greater strength 

 of the mandibles, and more fully developed muscular system of 

 the beetle, the insect is a more formidable enemy to the other 

 inhabitants of the water than the larva.* The Dyticidee, how- 

 ever, though naturally very voracious, are able to live some 

 weeks without food. The male is recognized by his smooth 

 elytra ; the female has furrowed elytra and a rough thorax. 

 The male, moreover, is readily distinguished by the form of 

 his fore feet, the two anterior tarsi of which are expanded into 

 a circular cavity on the under side, covered with a number 

 of suckers. The wing covers in both sexes are provided 

 internally with a pair of small membranes nearly circular, 

 aud ciliated at the margins, which some writers suppose are 

 instrumental in producing the humming sounds which they 

 occasionally make. The wings are large and at their an- 

 terior parts transversely folded beneath the elytra. These 

 insects have been observed to leave the water, and take to 

 flight. I never myself witnessed a specimen in the act of 

 flying. In the warm months the water-beetle may be seen 

 swimming in a pond or ditch, every now and then rising to the 

 surface, and protruding the tail portion of the body, so as to 

 admit the air through the opening elytra to the spiracles. 

 These extremely beautiful structures (see Fig. 2) are eighteen 

 in number, and are in connection with a system of* tracheal 

 tubes, which ramify in all directions through the whole system, 

 forming the respiratory apparatus. The surface of the back 

 underneath the wings is clothed with glossy brown hairs, 

 which by the repulsion of the water enables the admitted 

 air to gain free access to the spiracles. The last pair of legs 

 are fringed with long hairs, forming an oar-like apparatus, 

 by means of which the beetle is enabled to move about with 

 great swiftness in the water. It is a very interesting sight to 

 see the ease and rapidity with which a large water-beetle rows 

 himself out of harm's reach when disturbed as he lies at the 

 surface of the water. Well has Prof. Bymer Jones remarked, 

 "Nothing is, perhaps, better calculated to excite the admira- 

 tion of the student of animated nature than the amazing results 

 obtained by the slightest deviation from a common type of 

 organization ; and in examining the changes required in order 

 to metamorphose an organ which we have already seen per- 

 forming such a variety of offices, into fins adapted to an 



* Mr. Frank Buckland has lately drawn attention to the sad havoc these 

 water-beetles cause amongst young salmon, as witnessed by himself in a pond at 

 Hollymount Farm, Galway. See « The Field," of Not. 26. 



