THE CANADIAN ENTOMOLOGIST. 



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Fig. 14. 



quite freely. These larvae breathe through their tails, which they protrude 

 into the air for that purpose. When full grown and about to assume the 

 pupa state, the larva leaves the water, and burying itself in the earth, con- 

 structs there a round cell within which it undergoes its change, and if this 

 occurs in summer, it appears in two or three weeks as a perfect beetle ; 

 but if in autumn it remains in the chrysalis state all 

 winter, transforming to a beetle in the spring. 



Fig. 14 represents another of our large water 

 beetles, Hydrophilus triangularis. This species is 

 entirely black, and so strong and muscular as to be 

 difficult to hold in the hand when captured. The 

 relationship of this tiibe of insects ( Hydrophilus. \ 

 with the preceding one (Dytiscus) is very close. 

 There is much similarity of form and a close resem- 

 blance in habits ; their method of swimming, how- 

 ever, is different, for while in Dytiscus both paddles 

 are moved simultaneously, in Hydrophilus they are 

 moved alternately, hence the stroke of the latter is 

 much less effective. We are not aware that anything has been written on 

 the early stages of Hydrophilus triangularis, but in Europe the life history 

 of a closely allied species, Hydrophilus piceus, has been carefully traced 

 by several observers, and there is little doubt but that our species has 

 similar, if not identical habits. The female of H piceus has the singular 

 habit of spinning a silky cocoon for her eggs, one side of which is fur- 

 nished with an upright, bent, horny point, an inch long, which is supposed 

 to be serviceable in conveying air to the interior. These eggs, some fifty 

 or sixty in number, are placed in an upright position and in regular order 

 in their receptacle, which is round and flattened and attached to some 

 water plant at the surface of the water. In warm weather the larvae are 

 hatched in from twelve to fifteen days, when they escape at the lower part 

 of the cocoon, which is closed only by a few threads. They undergo 

 three moultings, and when full grown measure nearly three inches in 

 length. The head is horny and of a very singular form, its lower surface 

 being convex, while its upper surface is flattened. Us sharp and formid- 

 able jaws are well adapted for seizing and securing its prey. They are said 

 to attain their full growth in July, when they leave the water, bury themselves 

 in the earth, where they undergo their changes in a manner similar to that 

 of Dytiscus, 



