THE STRENGTH OF SPIDERS AND SPIDER-WEBS. 41 

 THE STRENGTH OF SPIDERS AND SPIDER-WEBS.* 



By HENRY C. McCOOK, D. D. 



T 



IHE frailty of a spider's web has passed into a proverb. Yet, 

 comparatively, the silken line of an orb-weaver is very 

 strong. According to Schaffenberger, it requires ninety spinning 

 threads of an Epeira to yield one thread of the thickness of a 

 caterpillar's thread ; and, according to Leeuwenhoek, it requires 

 eighteen thousand spider lines to make the thickness of a hair of 

 the beard. These comparisons are suggestive, although in a meas- 

 ure 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 num- 

 ber 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 hori- 

 zontal, must be strong enough to sustain the weight of a spider of 

 considerable size, such as Argiope cophinaria or Epeira insularis, 

 particularly when the female is heavy with eggs. 



Blackwell 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 half a 

 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 through the spiral meshes of a large snare, but generally 

 the threads are strong enough to hold them, in spite of their 

 struggles, 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 incasing armor of sil- 

 very dew, and has noticed how the spiral strings are bagged down 

 under the weight of the same (Fig. 1), must have inferred that the 

 snare was able to support a comparatively 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 orb-web. 



* Reprinted from Vol. I of American Spiders and their Spinning- Work, by the kind 

 permission of the author, to whom we are also indebted for the accompanying illustrations. 



