THE AERONAUTIC OR BALLOONING HABIT. 257 



could have been formed and fixed by heredity. The largest Orb weaver 

 that I ever saw taking flight was a partly grown Domicile spider about 

 the size of a marrowfat pea, say one-fourth inch long. After having 

 floated over a field and above a hedge row, it crossed a road and anchored 

 upon the top of a young tree. It never attained a height of over twenty 

 feet, but moved quite as fast as I could run. 



Young and small spiders fly rapidly, their motion depending, of 

 course, upon the state of the breeze, although they do not appear to 

 undertake their aerial voyage when the wind is strong. How- 

 ever, even when the air seems quite still to the observer, the 

 little aeronauts find a sufficient current in the height to which 

 they immediately ascend to bear them along with a good degree of speed. 

 Indeed, I have been surprised at the velocity of their progress in the 

 midst of what might be called a dead calm. 



Spider ballooning is not limited to a special period of the year, but 

 may be practiced at any time. In point of fact, however, the seasons 

 when it most prevails are the spring or early summer, and the 

 Seasons au t umn after the young have been hatched. The fall of the 

 ,.,. year is more especially the season for " flying spiders," and Oc- 



tober the month most favored.' But in early November also the 

 balloonists are abroad, particularly during the Indian summer, or when 

 a series of cool days is succeeded by a warm day. 



II. 



The following studies l were made during October, in fields adjacent 

 to Philadelphia and in the adjoining Delaware County. The days were 

 warm and bright, with a soft wind from the west, or a gentle breeze 

 blowing, but not steadily from any quarter. Stooping low and glancing 

 along the meadow, the eye caught the sheen of myriads of fine silken 

 filaments glistening in the sunlight. The tops of grass spires and the 

 bushy heads of tall weeds were netted together by innumerable threads, 

 and from many points of the same filaments were streaming out at 

 . various lengths into the air. Numerous small spiders, chiefly Orbweavers, 

 especially the young of Tetragnatha extensa, were rising from these plants 

 and sailing over the field. 



The finest exhibition of the aeronautic flight was seen along a post 



and rail fence which divided the meadow, and the description of this may 



be considered as covering the like behavior among all balloon- 



Eleva- jg^g scattered over the fields. The tops of the fence posts were 



* n r the favorite ascension points, and upon these clusters of young 



Lycosids were gathered, sometimes eight or ten in a group. The 



purpose in choosing these elevated spots is quite apparent, the currents of 



1 Proceedings Academy Natural Sciences, Philadelphia, 1877, page 308, sq. 



