1970] 
Eberhard — Fungus Gnats 
37i 
Larvae maintained apparently normal activity until just before 
they began to construct the pupal line. When four larvae were 
placed on a log in an observation chamber, two individuals which 
were to pupate 12 hours later could not be distinguished on the 
basis of the rate or type of their activity from the two which did 
not pupate. 
A series of probing movements (observed only once but probably 
performed in each case) immediately preceded line construction. The 
larva extended the anterior half of its body downward, perpendicular 
to the log’s surface, and waved it from side to side. It repeated this 
behavior several times, each time after raising itself back to the 
log’s surface and moving forward a centimenter or so. This probing 
behavior may be used to select appropriate pupation sites, informing 
the larva of any objects close below it. Pupae were never found 
where any such object could interfere with them as they swung on 
their lines. 
The construction of the pupal line took about 40 minutes. The 
larva first added silk to a long, relatively straight trail, and cut 
the silk along the edges of this trail, leaving only the central portion 
intact. It laid silk with bursts of a swinging motion which was less 
complex than the silk-laying movements described below. The larva’s 
head moved from the slime trail to one ventrolateral surface of 
segment 5 or 6 (abdominal segment 2 or 3) of its body (Fig. 4a), 
back to the trail, and then to the other side. Bursts of swinging 
often lasted 15 seconds or more, and the larva inched forward fol- 
lowing each burst. 
Larvae often cut silk just after moving forward: the head bent 
to the side of the trail, and moved slowly (usually forward) in a 
line nearly parallel with the trail. The threads encountered by the 
head were severed, and the central portion of the trail was progres- 
sively freed from the log’s surface and sagged down under the larva’s 
weight (Fig. 4b). 
At the ends of the trail, where the pupal line would be anchored 
to the log, the larva spent periods of up to 40 seconds in another 
activity, tapping its head rapidly against the wood (Fig. 4c). The 
taps were occasionally interrupted by swinging silk-laying movements. 
These swings occurred only singly and infrequently early in a burst 
of tapping, but occurred more often and in longer bursts toward 
the end. Tapping sometimes covered a relatively large area, and 
the pupal line was often split near its end, with each smaller line 
running to a different area of attachments. This pattern probably 
