THE BEETLES: COLEOPTERA 



47 



tected by a strong-smelling milky secretion which probably 

 renders them distasteful to fishes. They are able to dive to 

 escape danger, carrying down with them a small supply of air. 

 Beneath the surface of such ponds and pools as the whirli- 

 gig beetles frequent are to be found different species of div- 

 ing beetles (Dytis'cus, Fig. 31), which have adaptations 

 similar to those mentioned among the aquatic Hemiptera. 

 Thus in some the spiracles, which in land insects are along 

 the sides of the abdomen, are here placed beneath the edge 



Fig. 30. Whirligig beetles. (Natural size) 



of the wing covers on the back, and the space beneath the 

 wing covers is used as an air reservoir, which is replenished 

 with pure air by rising to the surface. In other species a 

 thin coating of air is carried on the under side of the abdo- 

 men. This supply is obtained by pushing the head above 

 water and capturing a bubble of air with the antennae, which 

 are quickly folded beneath the head, carrying the impris- 

 oned bubble to the under surface of the body. 



Scavenger Beetles. A useful part in the economy of na- 

 ture is played by the scavenger beetles (Necroph'orus, Fig. 

 32), large, black, red-spotted insects, which dig beneath the 

 carcasses of small animals, thus burying them beneath the 

 surface. The female then lays her eggs in the decaying ma- 

 terial, upon which the larvae feed until ready to transform. 



