94 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



lated with approximate accuracy. The example chosen was a snare of Epeira 

 sclopetaria five inches long by three inches wide, and the calculation showed a 

 total of 140,800. This is an orb of only medium size; in many webs the 

 number is certainly much larger, in some several times greater, although in 

 others it is doubtless greatly less. Blackwall calculated that a net of Epeira 

 apoclisa from fourteen to sixteen inches in diameter contained upwards of 

 one hundred and twenty thousand viscid globules. "Yet it will complete 

 its snare in about forty minutes if it meet with no interruption." 1 



That the viscidity of the spirals depends upon the beads, and that the 

 latter are placed upon the former, is of course proved by the effect of rain, 

 which separates the beads from the spiral line. But it may be also 

 Adhesive- s ] lown by scraping or rubbing off the globules with which the line 

 ness o ^ g g^-^ed. This leaves an inadhesive line, apparently of the 

 same constituency as the radii and other parts of the snare. An 

 easy way to demonstrate the fact is to insert a bit of glass beneath the 

 viscid portions of a web. The beads will adhere to the glass, if carefully 

 handled, so as to show distinctly the spiral strings in their proper relations 

 to the radii. By a little gentle manipulation with a camel hair brush or 

 other small object, the beads will be separated from their strings and melt 

 upon the glass, showing the string in the midst of the glutinous matter as a 

 straight silken thread. 



I feel well satisfied that the viscidity of the beads varies on webs of the 

 same species at different times, and it is probable that the degree of 

 viscidity is determined by the condition of the spider. When it is well 

 fed the secretions are abundant, but after long periods of fasting the 

 viscous quality of the secretion seems to be weaker, or the secretions being 

 less in quantity the amount distributed upon the lines is greatly dimin- 

 ished, and hence the effectiveness of the spiral strings is decreased. 



When exposed to the desiccating influence of the sun, and air briskly 

 agitated, the nets of geometric spiders lose their adhesive property ; 

 but when formed in situations from which the light is excluded, and 

 where the atmosphere is not liable to be perceptibly disturbed, they retain 

 their viscidity for a long period. Blackwall says that upon a net of 

 Epeira diademata constructed in a glass jar, which was placed in a dark 

 closet, where the temperature was not subject to great or sudden fluctuations, 

 the globules preserved their adhesive power almost unimpaired, and the 

 last formed spiral line its elasticity for more than seven months. 2 



I placed a snare of Argiope argyraspis in my study October 3d, 1882. 

 It was spun within a wooden breeding box, the front of which was covered 

 by a sliding glass door, the back by wire cloth. It was thus exposed to 

 light and air, in a well heated room. Examined as late as April 17th, 

 1883 (five and a half months after construction) the beads were found to 



1 Brit. Asscn. Reports, 1844, page 77. "Spiders of Great Britain," page 10, Introduction. 



2 Transactions Linn. Society, 1829, Vol. XVI., page 479. 



