TROPICAL AQUARIUM FISHES 161 
Water Strider (Hydrometride). 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 
Fic. 111. Water Strwer (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 (Hydrachna). These odd-looking little balls of intense red 
are sometimes placed in small tropical aquaria with fishes. This is in- 
Fic. 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 
Nc 
Fic. 113. ici eels 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- 
