1937] 
Case-building Instinct of Trichoptera 
131 
of it. In another instance a larva was supplied with plant 
bits only. Using these it formed a case, complete except for 
the flanges on the sides. The animal remained in the dish 
with plant bits for two days. No pieces of material were 
added during the second day. On the third the larva in its 
case was put into a dish containing sand. It at once began 
to add sand grains at the anterior end, at first on the hood, 
then at the edge of the tube proper. By the next day quite a 
good deal of sand had been added at the anterior end though 
the main part of the case was of the plant bits. Further 
investigation, however, is needed to indicate clearly the 
extent to which Molanna selects appropriate materials at 
different stages in the process of case-building. 
Summary 
1. The first steps in case-building, i.e., the formation of a 
girdle, are described both for a limnephilid and for Molanna. 
The method is quite different in the two species. 
2. Both the limnephilid and Molanna are able to employ 
a variety of unusual materials in the construction of their 
cases. 
3. Even when supplied with insufficient or unusual mate- 
rials, these caddis fly larvae build cases in close accordance 
with the method characteristic of the species. 
4. In the limnephilid there is little evidence that the 
animals select the more appropriate lengths of materials 
during early steps of case construction. As the case 
nears completion, however, considerable selection does occur. 
Incomplete evidence is presented of a similar situation in 
Molanna. 
Bibliography 
Betten, C. 1934. The Caddis Flies or Trichoptera of New York State. 
New York State Museum Bulletin. No. 292, pp. 1-576. 
Dembowski, Jan. 1933. fiber die Plastizitat der tierischen Handlungen. 
Beobachtungen und Versuche an Molanna-Larven. Zool. Jahrb. 
Abt. allg. Zool. u. Physiol., vol. 53, pp. 261-311. 
Gorter, F. 1929. Experiments on the case-building of a caddis-worm 
( Limnophilus flavicornis Fabr.) Tydschrift der Nederlandsche 
Dierkun dige Vereeniging. (3) vol. 1, pp. 90-93. 
Greene, M. J. and L. J. Milne, in press. Immature North American 
Caddis Flies (Trichoptera). 1. A summary and extension of 
our knowledge of these forms. 
Lloyd, L. T. 1921. The biology of North American caddis fly larvae. 
Bulletin of the Lloyd Library of Botany, Pharmacy and Materia 
Medica. No. 21, pp. 1-124. 
