TROPICAL AQUARIUM FISHES 159 
It is rapacious in extreme degree and is a good swimmer. A large ‘speci- 
men was once placed in an aquarium for observation. It so quickly 
attacked a goldfish that the scales fell in a small shower and the fish died 
before it could be rescued. The males may be distinguished by the ball- 
like development on the forelegs. They are usually of such a dark 
brown as to appear black, but are sometimes marked or bordered with 
yellow. 
Water Scavenger Beetle (Hydrophilide). We mention this beetle 
here because of its resemblance to the large predaceous diving beetle. It 
swims differently, using its legs alternately, while the diving beetle moves 
opposite pairs together. The Scavenger Beetle is also different in that 
Fic. 105. Water SCAVENGER BEETLE (Life size) 
it breathes at the surface from the mouth. Instead of long antenne they 
have palpi looking like club-shaped antenne. This beetle lives chiefly 
on decomposing vegetal and animal matter, although taking soft living 
plants such as Nitella. It has been claimed to be predaceous but there 
is doubt about their attacking fishes. They have been kept in aquaria 
with them without doing damage. On general principles, however, it is 
best to exclude all beetles, large or small. 
Giant Water Bug (Belostomatide) also known as the Electric 
Light Bug is one of our common bugs both on land and in water. Flying 
clumsily but strongly before electric lights, or patiently awaiting a victim 
at the bottom of a pond, the bug is one and the same. They are fiercely 
Fics. 106 anno 107. Grant Water Bucs (B. serphus and B. americana) THE 
SMALLER a Mate Wits Eccs on Back (Life size) 
