CHAPTER XXVI 

 ORDER TRICHOPTERA* 



The Caddice-Flies 



The members of this order have four wings; these are membranous 

 and usually more or less densely clothed with long, silky hairs. In the 

 more generalized members of the order, the venation of the wings corre- 

 sponds closely to that of the hypothetical primitive type with but few or no 

 accessory veins; in some of the more specialized members of the order, 

 the venation of the wings is reduced. The mouth-parts of adults, except 

 the palpi, are vestigial. The metamorphosis is complete. 



The caddice-flies are moth-like insects, which are common in the 

 vicinity of streams, ponds, and lakes, and are frequently attracted 

 to lights at night (Fig. 684). The larv^ of 



these insects are the well-known caddice- 



worms; these live in the water, and most of 

 them build cases about their bodies. 



In the adult insect, the body-wall is soft, 

 being membranous or at the most parch- 

 ment-like, and is thickly clothed with hairs. Fig- 684.— A caddice-fly. 

 The two pairs of wings are membranous 



and usually more or less clothed with long, silky hair. The fore wings 

 are denser than the hind wings and are often slightly coriaceous ; in 

 a few forms the wings are naked. The hind wings are shorter than 

 the fore wings; but they are usually broader; this is due to an ex- 

 pansion of the anal area of the hind wings. In a few species the hind 

 wings are reduced so that they are smaller than the fore wings ; in one 

 species the female is apterous, and in another the wings of the female 

 are vestigial. When not in use the wings are folded roof-lilce over the 

 abdomen. 



The posterior lobe of the fore wings is specialized as a fibula, 

 which is well developed in the more generalized forms, as Rhyacophila, 

 but more or less reduced in the more specialized genera. The costal 

 border of the hind wings is furnished with hamuli in some forms, as 

 in the Leptocerid^ and some Hydropsychidas. 



In the more generalized forms the venation of the wings cor- 

 responds quite closely with the hypothetical primitive type; this is 

 well shown by the wings of Rhyacophila fusctda (Fig. 685). The 

 more important modifications of this t}'pe shown by the wings of 

 Rhyacophila are the following: in the fore wing the tips of the second 

 anal vein and two of the branches of the third anal vein coalesce; 

 the subcosta bears an accessory vein ; this, however, is unimportant ; 

 accessory veins borne by the subcosta exist in only a few genera of 

 this order; the coalescence of veins Cu and ist A at the base of the 



*Trich6ptera: trichos (Opl^, rpTx^s), the hair; pteron {irrepdv), a wing. 

 (555) 



