THE ARMATURE OF ORBWEBS : VISCID SPIRALS. 



91 



Thus Fig. 86 will represent a section of a snare upon which an Orb- 

 weaver is spinning in her spirals. She has finished her task along the 

 beaded line, BL, and is working upon a line L. Just beyond it, imme- 

 diately behind her, the string numbered 5 shows a white unbroken surface ; 

 No. 4 is slightly ruffled; in the string No. 3 a few points of segregation 

 have begun to appear ; at No. 2 the beads are nearly perfected on the part 

 nearest the spider and quite finished on the further half. On string No. 1 

 the beads are completely formed. The figure, although sketched from na- 

 ture as far as it is possible to draw such swiftly changing objects, is neces- 

 sarily in part diagramatic. However, it accurately expresses the facts. 



The beads when newly formed are of a white color, translucent and 

 glistening. They are uniform in size, or nearly so, but there is a constant 

 tendency in the first-formed minute beads to undergo a further process of 

 aggregation, thus making 

 larger beads. These large 

 beads will often be found 

 at the crossing of the lines. 



The effect of rain upon 

 the beads is to blend sev- 

 eral into one until quite 

 large globules are 

 Beads forme d i n good 

 Dissolved . , .,, 



by Rains. P art mixed Wlth 



water. If the rain Fl _ c " ** 



be continued it dissolves the 

 viscid material, and the 



portions which do not drop off remain as large beads. These also soon 

 pass away, leaving the snare without the ordinary armature for efficient 

 service. I have frequently tested this matter during and after heavy or 

 long continued rains; and neither by tongue, nor touch of finger, nor con- 

 tact with other objects, nor by glass could the beads be discovered on many 

 of the spirals ; and often the whole web is disarmed. This accounts for 

 the fact that spiders find it necessary to construct new snares after pro- 

 tracted rains. The rain also dissolves, but not quite so freely, the thick 

 white shield and zigzag ribbon on the snares of Argiope. 



In this connection I introduce the explanation of a phenomenon which 

 long greatly puzzled me. While wandering in the woods of Delaware 



County, I observed on several separate occasions, always in the 

 ,. _ " snare of the Orchard spider (Argyroepeira hortorum), a novel and 



striking variation in the arrangement of the spirals, which is rep- 

 resented at Fig. 87. It will be seen from this figure that the spiral space 

 is divided into two distinct belts, of which the outer one contains about 

 half the number of lines in the inner one. Of two specimens showing this 

 appearance, the inner belt had sixteen and the outer eight, the difference 



illustrating the crystallizing of beads. SF, spiral 

 foundation ; BL, beaded line ; L, line just spun ; 2, 3, strings on 

 which beads are forming; SP, the spider. 



