130 
Psyche 
[June-September 
form a tube, open at both ends, and free from the substrate. With 
the first case complete, the larva is able to move about, pulling its 
house behind it, in search of food and resting places. This first case 
is about 1.5 mm long. The smallest individuals initially construct a 
case that is round in cross section, while the majority of individuals 
produce a somewhat flattened one. Larvae that fail to make cases 
never feed, and die within a few days. 
Case Enlargement 
As the larva grows and molts, it enlarges its case to 8-14 mm in 
length. Beyond the first instar, the case is always flattened, and is 
spindle-shaped in outline. 
In order to determine just how each instar contributes to the 
formation of the case, I provided two larvae with colored particles 
for case construction and, during each molt, replaced them with 
particles of a different color. Three colors were used: red (powdered 
brick), brown (sand), and black (iron removed from sand with a 
magnet). The discarded head capsules were collected after each molt 
to verify the molt and to obtain a measure of growth. 
To enlarge its case, the larva first adds a narrow band of new 
material to both ends. Then, beginning at one end, it slits the case 
open along one edge for a short distance, and widens it by adding 
extra silk and new particles which it picks up with its mandibles. 
The larva continues slitting the case and adding material along one 
side until it reaches the other end. It then adds extra material to that 
end and continues the process along the other side of the case (Fig¬ 
ures 6-8). 
Each instar, from the second through the next to last, adds once 
to the case as just described. The final instar adds a thin band of new 
material to both ends of the case, but does not widen it. 
Movements about the Habitat 
In order to follow the daily movements of individual larvae, I 
numbered the cases of 34 larvae in the bathroom of Barbour House 
on BCI using typewriter correction fluid (Liquid Paper®), and per¬ 
manent ink (Figure 9). The cases marked ranged in length from 3 
mm to 14 mm. Each was returned to its former location. The posi¬ 
tions of these larvae were noted at approximately twelve noon and 
twelve midnight daily for the following two and a half weeks. 
