32 GUIDE TO INSECTS. 



Sub-order SIALIDA. 



Table- The Sialidce or Alder-flies (1327-1334) have the head imbedded 



in the prothorax. The antennae are long and slender, composed of 



Fig. 32. 



Larva of Alder-fly (Sialis lutaria). 

 Enlarged. 



numerous joints. The prothorax is rather large. The front and 

 hind wings are of different shape, held roof-like when at rest, the hind 

 ones ample and folded when not in use. The tarsi have five joints. 

 Their metamorphoses are complete. The eggs of the common 

 British Alder-fly, Sialis lutaria, are laid on blades of grass, etc., 

 generally near water. The larva (fig. 32) as soon as it leaves the 

 egg makes its way to the water, where it spends most of its time in 

 the mud, feeding chiefly on other small aquatic larvse. The abdomen 

 is furnished with tracheal gills. When fully grown the larva leaves 

 the water and buries itself in the earth, where it turns to a pupa. 



Sub-order PLANIPENNIA. 



Table- rp ne nex ^ principal division of this order comprises the Plani- 



pennia, Snake-flies, Ant-lions, etc. These all have the head free 

 (except the Rhaphidiidce). The thorax is generally compact with 

 the prothorax small ; but in the Rhaphidtida, Mantispidce and 

 Nymphidce* the thoracic segments are more or less distinctly 

 separated, and the prothorax is larger. The four wings are nearly 

 or quite similar in form and size (except in the Nemopterida), held 



