120 The Under-Water World 



the less interesting. The Water Spring- 

 tails (Podura) are sometimes present in 

 such numbers as to form black masses on 

 the surface of ponds. If these minute 

 creatures are disturbed the mass breaks 

 up, each individual leaping away to 

 safety ; but the mass is quickly reformed 

 as soon as the danger is past. The 

 bodies of these insects, and others of the 

 surface-film fauna, are covered with very 

 short and closely-set hairs that prevent 

 the body from becoming wet. A spring- 

 like apparatus on the underside of the 

 body of Podura enables it to leap actively. 

 The Skaters (Hydrometridce) are well 

 known as they are to be seen during the 

 spring and summer months disporting 

 themselves very actively on ponds and, 

 in some cases, on quite swiftly flowing 

 streams. There are several forms, for 

 the most part small insects. The food 

 is mainly dead insects found floating on 

 the surface of the water. 



