34 



THE BOOK OF NATURE STUDY 



hollowed ready for a vigorous stroke, the head directed down- 

 wards, and the eyes, of which there are six on each side, ever on 

 the lookout for victims. At the extreme tip of the abdomen 

 are two spiracles leading into large tracheal tubes which run for- 

 ward in the body. Through these openings respiration is carried 

 on while the animal hangs at rest. The seven pairs of spiracles 

 which are visible on the sides of the body do not become func- 

 tional until the pupal stage is reached. 



When the larva is full fed it leaves the water and buries itself 

 in the moist soil near the margin. Here it constructs a rounded 

 chamber, then casts its skin and becomes a pupa. 

 In this stage it is shorter and broader than it was 

 when a larva, and exhibits through the thin trans- 

 parent cuticle of the pupa the limbs and other 

 parts of the imago. If pupation takes place in 

 summer time the perfect beetle emerges in about a 

 fortnight ; but if later in the year, then hibernation 

 takes place, prolonging the pupal stage till the 

 following spring. In either event the full-formed 

 beetle is at first soft and of a pale colour ; nor does 

 it attain its final aspect until several days have 

 elapsed. Although provided with strong jaws, the 

 perfect insect relies for defence upon an evil-smelling 

 milky fluid which can be discharged from glands 

 situated in the front part of the thorax, and upon a yellow am- 

 moniacal liquid secreted by a pair of glands at the end of the 

 abdomen. 



BIBLIOGRAPHY. Miall, Natural History of Aquatic Insects ; Furneaux, Life 

 in Ponds and Streams ; Cambridge Natural History, vol. vi. ; Fowler, The Cole- 

 optera of the British Isles, 5 vols. ; Rye, British Beetles. 



FIG. 20. Pupa 

 of Dyticus. 



