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STRENGTH OF WEBS AND POWER OF SPIDERS. 231 
centre when the web is quite round, but otherwise is elevated above the 
centre; sometimes is placed well to one side. (Fig. 217.) Its width, though 
subject to variation, may be said approximately to equal one-third of 
the central space. 
The frailty of a spider’s web has passed into a proverb. Yet, compara- 
tively, the silken line of an Orbweayer is very strong. According to Schaf- 
enberger! it requires ninety spinning threads of an Epeira to yield one 
thread of the thickness of a caterpillar’s thread; and, according to Leeu- 
wenhoek, it requires eighteen thousand spider lines to make the thickness 
of a hair of the beard. These comparisons are suggestive, although in a 
measure deceptive, since there are vast differences in the size of the threads 
woven by Epeiroids. It is probable that the extraordinary strength of the 
thread is due to the superposition of a large number of extremely minute 
threads. However, after the thread is woven, Meckel could not recognize 
it as consisting of more than eight to ten strands. A geometric snare, 
whether vertical or horizontal, must be strong enough to sustain the weight 
of a spider of considerable size, such as Argiope cophinaria or Epeira insu- 
laris, particularly when the female is heavy with eggs. 
Blackwall thus determined by experiment the strength of a line by which 
a female Epeira diademata, weighing ten grains, had sustained itself from 
a twig. He attached to the extremity of the line a small piece of muslin 
with the corners nearly drawn together, so as to form a minute sack, into 
which he carefully introduced sixty-one grains weight in succession, being 
more than six times the weight of the spider. On the addition of one-half 
grain more the line broke.? 
Not only must an orb sustain the weight and movements of its maker, 
but it must also have sufficient strength to hold the various insects which 
strike upon it. Bees and wasps are sometimes able to break 
ee through the spiral meshes of a large snare, but generally the 
and Dews threads are strong enough to hold them, in spite of their strug- 
gles, until the proprietor can enswathe them. Moreover, the orb- 
web must be able to sustain the weight of evening dews. One who has 
seen such snares in the early morning, when every viscid bead appears to 
have attracted to itself an encasing armor of silvery dew, and has noticed 
how the spiral strings are bagged down under the weight of the same 
(Fig. 218), must have inferred that the snare was able to support a com- 
paratively heavy burden. The same is true concerning summer showers, 
which must fall very heavily and be driven before a pretty strong wind 
in order to batter down a well constructed orbweb. 
Indeed, I have often wondered at the capacity of these fragile structures 
to resist the force of winds. Here, for example, are webs of Epeira strix 
1 As quoted by Meckel. 
* Transactions Linnean Society, Vol. XVIII, 1841, page 321. 
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