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 Orbweaver is very strong. According to Schaf- 

 enberger l 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. 2 



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 

 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. 



2 Transactions Linnsean Society, Vol. XVIII., 1841, page 321. 



