concentrate in the same place, but become widely distributed. Some larvae 

 show a positive heliotropism during this period and concentrate in the light 

 part of the aquarium (Triaenodes bicolor). 



Some larvae of Annulipalpia which are without cases (Rhyacophilinae, 

 Polycentropodidae) are able to swim during their whole larval life; if such 



a larva is disturbed, it holds itself in 

 the water by extending its legs and moves 

 by curving movements of the abdomen; 

 these movements resemble (e. g., in 

 Rhyacophila) the movements of a 

 leech; however, the movements of these 

 larvae are less smooth and weaker. Full- 

 grown larvae of some Hydroptilidae with 

 light cases built of secretion (A gray- 

 lea, Oxyethira), are also able to 

 swim; they move slowly in stagnant 

 water by rowing movements. 



The larvae of Limnophilidae cannot 

 swim. The larvae of species of this 

 family which lay their eggs outside the 

 water (Figures 81—83) are able to move 

 on land when they hatch from the egg; 

 they crawl on the egg mass and then 

 over humid ground or on objects 

 projecting from the water, seeking water. 

 The same has also been observed in the 

 family Sericostomatidae, e. g., in 

 Notidobia ciliaris (Siltala, 

 1907:338). 



Respiration. With the exception 

 of larvae of species (Enoicyla) which do not live in water, and except 

 for short periods spent on land when the larvae of some species hatch 

 from the egg, caddis fly larvae spend their life in water, where they live 

 on the bottom or among vegetation; like other aquatic insects with a 

 closed tracheal system, they breathe oxygen dissolved in water. 



In the early stages oxygen is absorbed through the thin integument of the 

 whole body; later, respiratory areas become differentiated; they are 

 distinguished by the permeability of the integument and by their light color; 

 most larvae also develop special respiratory organs, the tracheal gills. 

 Species with tracheal gills also have cutaneous respiration, which is proved 

 by the fact that the insect continues to live after the amputation of the 

 tracheal gills. 



The larvae of Trichoptera are very oxyphilic and cannot live in water 

 with a low oxygen content; larvae living in flowing water use the current 

 to change the water; those living in cases create an artificial current inside 

 the tube by undulating movements of the abdomen which carry the water 

 through the case. These movements should be regarded as respiratory 

 movements. Free-living mobile larvae living in flowing water do not make 

 respiratory movements; however, when placed in an aquarium, they settle in 

 one place and before they die, begin to make undulating movements with their 

 whole body, like the movements of case -bearing species. 



FIGURES 78 and 79. Movement of young 1st 

 stage larva (after Siltala): 



78 — Oxyethira sagittifera 

 raylea mul tipunc ta t a. 



79 -Ag- 



48 



