The threads lose elasticity several days after completion of the nets, 

 and have to be replaced. The larva thus continues to build at night during 

 the whole functional period of the net, without increasing the length of the 

 net; it repairs damage and lays new threads on the inside, beginning from 

 the anterior margin of the dwelling chamber and continuing toward the 

 entrance to the funnel. This activity of the larva ensures the elasticity of 

 the net during the whole time of its existence (about 6 weeks); if the outer 

 wall of the net wears off, new walls of the funnel are constantly woven on 

 the outer surface. 



While the funnel is still incomplete, plankton falls on the net and is 

 caught by the larva; this provides food during the whole weaving process. 

 The larva builds a capturing net from its first stage and continues to do so 

 during its whole later development; the net of a freshly hatched 1st stage 

 larva is 4 — 6mm long (Brickenstein, 1955:6—44). 



Sattler observed the weaving of the nets of the larvae of Hydropsyche 

 angustipennis and of three other species (H. instabilis, H. pellu- 

 cidula, H. fulvipes) in nature and in an experimental vessel with stones 

 at the bottom (Figure 179) and with an artificial water current; the process 

 of weaving could be observed distinctly through the walls of the vessel 

 (Sattler, 1958). These observations were repeated many times, but no 

 83 difference was found between the nets of the species observed. Sattler's 

 observations were made on mature larvae. 



The net of Hydropsyche consists of a dwelling chamber, a capturing 

 net and an entrance "hall" to each (Figure 124, A). The larva selects a 

 suitable place for the dwelling chamber in a hollow among stones; it then 

 attaches the supporting threads which determine the length, width and height 

 of the chamber; the length of the case is determined by the length of the 

 larva; the width and height of the case are determined by threads drawn by 

 the larva perpendicular to its body, near its upper and lower level, at the 

 ends of the chamber; the weaving of the dwelling chamber begins from the 

 front; it is woven alternately from the anterior or posterior end; the 

 weaving ends in the middle of the case, where the anterior and posterior 

 parts of the net meet; the walls of the chamber are covered on the outside 

 with minute sand grains connected by zigzag sutures (Figure 124, B). After 

 completion of the dwelling chamber, the larva weaves the entrance hall, 

 enclosing a small space near the chamber by dome-shaped or less regularly 

 built walls of sand grains, which are more or less strongly glued together. 



The weaving of the capturing net begins with the preparation of a frame; 



the larva may use objects in the vicinity for this, such as stones or twigs; 



if these are not available, the larva weaves a round or less regular frame; 

 84 ■ i 



this is attached to surrounding objects, and its margins are framed with 



leaflets or detritus. The weaving of the net is rapid and is performed in 

 a strictly definite order. Unlike the larva of Neureclipsis which runs 

 from one side to the other, the larva of Hydropsyche weaves its small 

 85 net while it remains in one place. The larva then occupies a position in the 

 middle, near the base of the frame; it begins weaving from the bottom; it 

 attaches the 1st thread to the circumference of the frame and draws it to 

 a point near the middle of the base (Figure 125); the 2nd thread is placed 

 in a similar direction and sequence, but from the other side; it is glued to 

 the 1st thread at their intersection; both threads become curved at the 



77 



