TROPICAL AQUARIUM FISHES 



161 



Water Strider (Hydromctridcc). Another of the predaceous aquatic 

 insects is the Water Strider. Quite as well known as the Whirligig 

 Beetle, it adopts somewhat the same methods of securing its prey, darting 



Fig. 111. Water Strider {Life size) 



over the surface of the water, waiting for the stream to bring down some 

 helpless insect victim that has fallen overboard. They are capable of 

 catching young fishes which come to the surface. 



Mites (HydracJma). These odd-looking little balls of intense red 

 are sometimes placed in small tropical aquaria with fishes. This is in- 



FiG. 112. Water Mite (Enlarged about four diameters) 



advisable, as they are parasitic. It is doubtful whether they actually kill 

 their host. They are common in the still water of lily ponds. 



Hydra. Although Hydra is not an insect we include it here as an 

 important enemy of young fishes. Hydra is a polyp which attaches itself 

 to plants, stones or the sides of the aquarium. Being thread-like in ap- 

 pearance it is apt to be overlooked, especially by the inexperienced. It 



Fir.. 113. Hydra (Greatly enlarged) 



is usually introduced with living food caught from pools. The spores are 

 so small as to be unrecognizable, and therefore they cannot be avoided. 

 The animal itself has a cylindrical body with from 5 to 12 tentacles sur- 



