42 Descriptive Zoology. 



The Fireflies. These, too, are beetles. Children do not need to 

 be told that they emit light, and the most learned scientist cannot tell 

 just how the light is produced. The females of some fireflies are wing- 

 less, and are called " glowworms. 1 ' 



Water Beetles. Not least interesting among beetles are the water 

 beetles. We shall notice three kinds. First, the whirligig beetles, 

 which nearly everybody has observed on the surface of the water, whirl- 

 ing round and round in swarms. Like the other water beetles, they 

 have a flattened body, and the hinder legs are paddle-shaped. The 

 whirligig beetles occasionally dive. They have each eye divided into 

 two parts, one of which looks up and the other down, so that one would 

 say they had two pairs of eyes. 



The predaceous diving beetles have oval bodies, somewhat wider 

 behind. They are more abundant in stagnant water. When at rest 

 they come to the surface and remain with the head down and the tip of 

 the abdomen projecting into the air. Like the water bugs, they breathe 

 by taking air under the wings, and when a new supply is needed they 

 again come to the surface. The spiracles are on the upper surface of 

 the abdomen. They are very voracious, and eat other insects and even 

 small fishes. The larvae are spindle-shaped, with sharp, incurved 

 mandibles, and are known as " water tigers " on account of their fierce- 

 ness. Both larvae and adults may be kept and fed on meat. 



The water scavenger beetles are elliptical. They do not breathe as 

 do the predaceous water beetles, but come to the surface head up and 

 take air under the body, where it is carried as a film, which gives a sil- 

 very gleam when seen from beneath. They are supposed to feed mainly 

 on decaying vegetable matter, but some are known to catch live insects 

 and eat them. They may be distinguished from the predaceous water 

 beetles by their shape, and by a long, sharp spine that projects back- 

 ward from the under surface of the thorax. Catch one of these beetles 

 by one of the hind legs and you will probably find out the use of this 

 spine. Though all these beetles have the power of flight, they do not 

 usually try to escape from a jar of water. It is easy to catch them by 

 scooping in ponds with a dip net. They may be kept in glass jars 

 (candy jars are very convenient), and watched from below as well as 

 from above. If they have no solid surface on which to crawl, they are 

 not likely to get away. It would seem that they cannot start to fly 

 from the surface of the water, but must have some solid object from 

 which to rise into the air. 



