FIELD BOOK OF PONDS AND STREAMS 



black beetles — the hydrophilids or water scavengers — which 

 look and act very much like them. 



Adults. — But although they are similar there are several 

 ways in which the adults of these two families can be distin- 

 guished. H^'drophilids hang at the surface with heads up 

 (Fig. 212), dytiscids hang with heads down (PI. X). Hydro- 

 philids have very short club-shaped antennae and long 

 slender palpi which may easily be mistaken for antennas 

 (Fig. 212, 2), dj^tiscids have slender thread-like antenna 

 (Fig. 209). When adult hydrophilids come to the surface, 

 they thrust their antennae through the surface film and pull 

 back a bubble of air which spreads over the ventral surface 

 of the body like a silver blanket. 



Eggs and larvae. — They lay their eggs in beautiful silken 

 cocoons, often fastened beneath floating leaves of water 

 plants (PI. XVII). Sometimes the cases are carried beneath 

 the mother's body. They are all waterproof and contain 

 about a hundred eggs but the young larvae eat one another so 

 lustily that the final crop is reduced. 



Fig. 212. — Water scavenger, Hydrophilus: 

 adult, ventral side; 2, larva, dorsal side. 



I, 



274 



