AQUATIC INSECTS 



although no insect looks more gentle and satisfied, none is 

 more fierce and voracious. 



They abound in ponds and pools and in the weed-grown 

 side waters of streams. Some are only a few hundredths of 

 ' an inch, others are an inch and a half long. Among them are 

 some of the largest insects which live in the water, but, big 

 and little, they constitute a population of blood-thirsty pred- 

 atory animals. 



They are black or brownish-black, often marked with dull 

 Yellow, and have slender thread-like antennae (Fig. 209). 

 By these they can be distinguished from the hydrophilids, 

 another large family of beetles, whose antennae are club- 

 shaped and carried hidden in a pocket when they dive (Fig. 

 212). In some genera the males have clinging organs on the 

 front feet; these are pressed down upon the smooth wing- 

 covers of the female and act as clasping organs during mating 

 (Fig. 208 and Fig, 209). Like many other water-beetles 

 dytiscids have flattened hind legs which they use in swimming. 

 Before diving they lift their wing-covers allowing air to enter 

 the space beneath them into which their spiracles open. This 

 is their diving supply and with it they can remain under water 

 a long time. 



Eggs. — The females puncture the surfaces of submerged 

 leaves and lay their eggs singly in the plant tissues. 



Larvae. — The larvae are the water tigers, a truly descriptive 

 name for them and their habits (Fig. 209)-; When a water 

 tiger catches sight of a promising young dragonfly it immedi- 

 ately rears up and stands at rigid attention with wide open 

 mandibles. When the dragonfly comes near enough the beetle 

 lunges forward and clutches its prey between its sickle-shaped 

 jaws. These jaws are hollow and with its mouth still closed, 

 the beetle can suck the body juices of the dragonfly while 

 still keeping its firm clutch. It breathes air and has a pair 

 of spiracles at the rear end of its body which it thrusts up 

 above the surface whenever it comes to the top. 



267 



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