372 
Psyche 
[September 
functions to anchor the pupal line more securely by allowing an 
increased area of attachment. 
One other kind of behavior occurred on portions of the trail which 
hung free of the log. The larva drew its head slowly along the 
line (Fig. 4d), moving its mouthparts rapidly and apparently either 
packing the strands together or eating away some strands of silk. 
These “trimming” movements often resulted in a perceptible thin- 
ning of the line. 
The four types of behavior — swinging, cutting, tapping, and 
trimming — were interspersed throughout most of the construction 
of the pupal line. Cutting and tapping were more frequent during 
the early stages, and most of the trimming which occurred during 
this time was done as the larva backed slowly away from a tapping 
(attachment) site. The larvae were able to turn around on the 
pupal line by crawling back on themselves just as they did while 
on their sheets (Fig. 4c), and occasionally ceased work at one end 
of the line, turned around, and began different behavior somewhere 
else on the line. 
When the line was completely or nearly completely free from 
the sheet, the larva positioned itself near the center and made final 
spinning movements which lasted two to three minutes. These 
movements differed from the swinging movements of line construc- 
tion only in that the silk was now laid from the pupal line to a 
dorsal section of the larva’s body. The head swung farther and 
farther over the back, eventually crossing the dorsal midline of seg- 
ments 5 and 6 with each swing. This behavior produced a small 
collar of silk which anchored the larva’s body to the pupal line 
(arrow in Fig. 5a). Larvae inched themselves forward along the 
line as they spun the collar; the distances they moved varied, and thus 
the number of segments anterior to the collar and free of the pupal 
line varied. 
The larva trimmed the line near its head for a short time after 
fastening itself into position on the pupal line, but soon the head 
movements diminished, and the segments anterior to the collar 
sagged away from the line and hung below the rest of the body. 
Segments 4-12 began a series of contractions, and segments 1 and 2 
(thoracic segments 1 and 2) swelled. The contractions occurred 
approximately every 15 seconds at first, but soon slowed considerably. 
As segment 1 expanded, it began to engulf the head capsule, and the 
larva flexed the capsule ventrally during the contractions so that its 
ventral surface lay against the ventral surface of segment 1 (Fig. 5a). 
