SOME AQUATIC INSECTS 85 



a number of curious circular, cement-secreting 

 organs, somewhat similar to those on the front 

 legs of the male Dytiscus, and used for the same 

 purpose. The third pair are paddle shaped, 

 broad, and capable of delivering powerful back- 

 ward strokes as the insect swims through the 

 water. The middle pair of legs are also used 

 as paddles, but are not so broadly expanded as 

 the third pair. The Whirligig Beetles make 

 a curious squeaking noise just before taking 

 flight, the sound being produced by rubbing the 

 under side of the wing-cases against the end of 

 the body. The beetle does not rise directly 

 from the surface of the water in its flight, but 

 first climbs up a plant stem, and then spreads 

 open its long wings. When collecting Whirligig 

 Beetles, it is necessary to handle them with 

 caution, as when alarmed they exude from every 

 joint of their body a milky fluid which smells 

 most unpleasantly like cockroaches. They are 

 most amusing and interesting little insects to 

 keep under observation, but the aquarium in 

 which they are confined should have its top 

 covered with a gauze cap, or otherwise they 

 will, after a good deal of struggling, probably 

 climb up the glass and take flight. 



During the summer nearly every weed- 

 grown, shallow pond, covered with a green 

 mantle of duckweed, will be found to contain 

 a rather pretty, small and glossy-black beetle 

 called Hydrobius. Its under surface is over- 

 spread by a bubble of air, giving it a silvery 

 appearance; while its method of rising head- 

 first, and poking one side of the head and thorax 



