520 
THE STUDY OF INSECTS. 
difficult to catch them without a net. Many of them when 
caught exhale a milky fluid having a very disagreeable odor. 
They feed upon small flies, beetles, and other insects that 
fall into the water, and are furnished with well-developed 
wings, with which they fly from one body of water to an¬ 
other. 
This is one of the most easily-recognized families of the 
whole order Coleoptera. The members of it are oval or 
elliptical in form (Fig. 634), more or less flattened, 
and usually of a very brilliant, bluish-black color 
above, with a bronze metallic lustre. The fore 
legs are very long and rather slender; the middle 
Fig. 634. and hind legs are short, broad, and very much flat¬ 
tened. These insects are remarkable for having the eyes 
completely divided by the margin of the head, so that they 
appear to have four eyes—a pair upon the upper surface 
of the head with which to look into the air, and a pair upon 
the under side for looking into the water. The antennae 
are very short and peculiar in form. The third segment is 
enlarged, so as to resemble an ear-like appendage, and the 
following ones form a short, spindle-shaped mass. They 
are inserted in little cavities in front of the eyes. 
The eggs of these insects are small, of cylindrical form, 
and are placed end to end in parallel rows upon the 
leaves of aquatic plants. The larvae (Fig. 635) are 
long, narrow, and much flattened. Each abdominal 
segment is furnished with a pair of tracheal gills, 
and there is an additional pair at the caudal end of 
the body. The elongated form of the body and the 
conspicuous tracheal gills cause these larvae to re¬ 
semble small centipedes. When a larva is full 
grown it leaves the water and spins a gray, paper¬ 
like cocoon attached to some object near the water. 
The pupa state of the species in which it has been 
observed lasts about a month. 
The family is a small one. At present only thirty-six 
