Orbs -with 



126 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



11. 



The third group of Orbweavers making vertical webs is composed of 

 those which retain the open hub. Among these are our indigenous species 



of the genus Acrosoma. These are found in the neighborhood of 



Philadelphia, and are distributed very generally throughout the 

 Hubs Middle, Northern-Middle, and Southern States, east of the Rocky 



Mountains. The favorite site for their snares is a large open 

 space between two bushes or trees, or between the diverging branches of 

 the same. I have most frequently found them in the margins of an open 

 grove, wood, or forest. As a rule they swing their nets at a considerable 

 height, so that one's face comes in contact with them while passing through 

 the woods. The foundation lines are frequently of considerable length, four 

 or five feet, or even more. The delicate orb swung between them is a very 

 pretty sight as one sees it outlined against the sky, showing through the 

 vista of the opening trees. (Fig. 111.) 



The three species common to our neighborhood are Acrosoma rugosa, 

 spinea, and mitrata. ^ They are all characterized by abdomens which present 



upon the dorsal surface spines of greater or less length and hard- 

 ^avorite j^ggg^ These spines are more decidedly developed upon the first 



two named species. In the last named species, the Mitred spider, 

 the spinous processes are small, and the integument is not so tough. 



All the three species make substantially, and I might say almost pre- 

 cisely, the same sort of web. The shape of the snare is usually quite orbic- 

 ular, nearly always approaching a circle more nearly than that of most 

 species of Orbweavers. The number of radii is very great, amounting at 



times to as many as eighty, and the number of spirals is corre- 

 f^^^° spondingly large. The orb itself is not very large, generally 



being w^ithin six inches in diameter rather than above. It re- 

 sults, therefore, that the spiral space presents a remarkably close texture of 

 checkered openings between the cross lines. The free zone, which in the 

 typical Epeira net contains no lines crossing the radii, is always occupied 

 in this genus by the lines of the notched zone, which wind in three or four 

 comparatively widely separated concentrics through the entire free zone. 

 These take the place of the notched zone of the Epeira orb, whose con- 

 centrics are wound close uj) to the hub. 



The hub, as has been stated, is always open, and within it the spider 

 is usually found hanging with its legs outstretched, grasping the marginal 

 circumference of the hub. Spinea and Mitrata hang in a })Osition closely 

 resembling that of the ordinary Epeira, that is to say, with the head 



^ Ah 1 have lieretofore shown (Proceed. Acad. Nat. Sci. IMiilada., 1SS8, pajje 5), the luinieis 

 of these species as given by Walckenaer are entitled to ])riority. They will i)rohably be 

 known respectively as Acrosoma gracilis (rugosa), A. saggittata (spinea), and A. re(hivi;ui:i 

 (mitrata). 



