COLEOPTERA. 
523 
Family DYTlSCiDvE (Dy-tis'ci-dae). 
The Predaceous Diving-beetles 
If one will approach quietly a pool of standing water, 
there may be seen oval, flattened beetles hanging head 
downward, with the tip of the abdomen at the surface of 
the water. Such beetles belong to this family. 
The predaceous diving-beetles are usually brownish 
black and shining, but are often marked indefinitely with 
dull yellow. They can be distinguished from the water 
scavenger-beetles, which they resemble in general appear¬ 
ance, by the thread-like form of the antennae. The hind 
legs are the longest, and are fitted for swimming, being flat¬ 
tened, and fringed with hair. The middle and the hind pairs 
of legs are widely separated. This is due to the very large 
hind coxae which cover the greater part of the lower surface 
of the thorax. In the males of certain 
genera the first three segments of the fore 
tarsi are dilated and form a circular disk* 
upon the under side of which are little 
cup-like suckers (Fig. 630). In a few 
cases the middle tarsi are dilated also. 
The females of some species exhibit an 
interesting dimorphism in that some of the individuals have 
the elytra furnished with a number of deep furrows (Fig. 
631), while others of the same species have them 
smooth. 
The diving-beetles abound in our streams 
and ponds, but they are more often found in 
standing water than in streams. When at rest 
they float in an inclined position, head down- 
Fic. 631. W ard, with the tip of the hind end of the body 
projecting from the water. The spiracles open on the 
dorsal side of the abdomen beneath the elytra. By lifting 
the elytra slightly a reservoir is formed for air, which the 
beetle can breathe as it swims through the water. When 
