i 9 o THE BRITISH NATURE BOOK 



where they prey on other creatures. When full fed they leave the water and 

 burrow in the earth, where they pupate, eventually changing to the perfect 

 insect about midsummer. The Common Alder-fly is Sialis lutaria. Snake- 

 flies (Raphididce) are recognized by their large heads and long necks, these 

 and the thorax having a distinct snake-like appearance. There are four 

 British species ; the larvae live in rotten wood or under bark and prey upon 

 small insects, throwing themselves when alarmed into very grotesque positions. 

 Lacewing-flies. These are pale green, with beautiful eyes of a metallic 

 lustre, and are to be encouraged, for the larvae feed on aphides, from which 

 they suck the juices. The eggs are most remarkable objects, each on a long 

 stalk, and laid in clusters. The female lays on the leaf or twig a drop of sticky 

 substance, and draws it upwards into a thread, at the top of which the egg is 

 attached. Some of the larvae cover themselves with the dried bodies of the 

 aphides on which they have fed, thus obtaining a protective device which 

 effectively conceals them from their enemies. 



