RL a ee ell 
ENGINEERING SKILL OF SPIDERS. 225 
radiating supports seized the margins. These structures, modified as they 
doubtless were by their environment and in a measure thus compelled to 
their final form, evidently show considerable skill in adapting spinningwork 
to circumstances. 
There is no doubt that in the ordinary operations of snare making and 
nest building, the Labyrinth spider continually brings into play certain 
principles of operation which may be properly designated by the 
term engineering. For example, in looking at Labyrinthea work- 
ing up the maze of crossed lines in which her domicile is hung, 
one is continually impressed with the fact that she so balances 
and adjusts the lines as they are successively spun out, that the whole 
spinningwork is as 
well suited to its 
purposes as is the 
complex scaffolding 
used by human car- 
penters in building 
a house. I cannot 
conceive in what 
manner the spider 
perceives the vari- 
ous inequalities, on 
this side or that, 
which require spe- 
‘cial treatment in 
the way of staying, <,% 
tightening, adding, ~=& = 
ete. Perhaps her ~— 
sense of touch is 
so delicate that her 
perception of these 
necessities is accurate enough to enable her to construct her intricate snare 
so as to attain precisely the same results as would have been reached had 
she been guided by an engineering intention from the very first. 
Again, Labyrinthea is in the habit of roofing her silken tent with a 
leaf. Sometimes the leaf is used in lieu of the tent, and again the tent 
is woven-inside of the concavity of the leaf. In order to ob- 
serve the mode of treatment I once dropped a curled leaf into 
a newly made snare of this spider. She at once perceived its presence by 
the agitation of the maze, ran to it, and appeared immediately to perceive 
its value. She fastened to it here and there a line, as though to preserve 
it from falling farther and thus damaging her snare. She then ran to 
the stem, attached a strong thread to it, and clambered out upon her silken 
trestle for the distance of two inches, and then fastened her line, leaving 
Labyrinth 
Spider’s 
Snare. 
a 
N 
Lio 
Fig. 2138. Globular structure of young Theridium tepidariorum. 
Roofing. 
