SIMULIUM : EARLY STAGES 175 



spines at their inner ends as well as long delicate hairs ; the max- 

 illae are somewhat triangular plates of chitin, densely covered with 

 hairs arranged in a tuft, and usually with one slender spine just below 

 their apices. The palpi are short, consisting of three joints. The labial 

 plate may be broad or narrow, and is armed at its anterior end with three 

 to five or more teeth, the external ones usually bidentate ; these teeth are 

 useful in identifying the species. The alimentary tract of the larva is 

 a simple tube, at either side of which there are two long glands, which 

 secrete the gelatinous substance from which the anchoring threads and 

 the silken fibres of the cocoon are made. When the larva is about to 

 pupate, it spins the characteristic case by first fastening a thread on one 

 side of its support, and then carrying the other end over to the opposite 

 side ; repeats the process until it has constructed a heart-shaped 

 pouch, deeply scooped out at its anterior end, and pointed posteriorly ; 

 this is attached by its sides to the support, which may be the back of 

 a leaf or twig, or the surface of a stone. 



Miss Phillips has made some detailed observations on the spinning 

 of the cocoon of Simulium pictipes, Hagen, which she describes as 

 follows : ' In spinning, the thread issues from the mouth and is placed 

 ' in the different positions by the thoracic proleg. The head is bent 

 ' down, and with the proleg the thread is drawn around the body and 

 ' other threads placed or twisted in all directions, until a very irregular 

 ' network is formed, covering the whole of the body, except the head. 

 ' The skin of the head is then cast off, and the insect pulls itself out 

 ' of the skin of the body, leaving it whole. The cast skin may often 

 ' be found in the cocoon, with the pupa. The cocoons are commenced 

 ' at the upper margin and spun continuously down to the caudal end, 

 ' where several threads are drawn from the cocoon and attached to the 

 ' last one or two of the body segments of the pupa. The threads hold 

 ' the pupa very firmly, and are always found when the pupa is pulled 

 ' out of its case.' 



The larvae feed on small crustaceans, such as Copepods and Isopods, 

 small polyps, fresh water sponges and small animalculae, which are present 

 in all streams. Their movements are interesting to watch when crowded 

 together on a leaf. When a larva sways too much to one or other side, 

 and touches its fellow, both rapidly retract. They can crawl up their sup- 

 ports with great agility, the loops being rapidly made. Before it moves 

 the larva always fixes its thread to the support so that if it becomes 

 detached it can crawl back in safety. 



The pupa (Plate XXXII, fig. 3) is ovoid in shape the anterior end 



