THE WHITE-OAK GALL-FLY. 547 



VIII. Fig. 10.) Its head and thorax are black, and are 

 rough with numerous Httle pits and short hairs ; the hind 

 body is smooth, and of a shining pitch-color ; the legs are 

 dull brownish red ; and the fore wings have a brown spot 

 near the middle of the outer edge. Its body is nearly one 

 quarter of an inch long, and its wings expand five eighths 

 of an inch. 



A dwarf oak (^Quercus infectoria), growing on the borders 

 of the Dead Sea, produces galls somewhat like the forego- 

 ing, which have been supposed to be the apples of Sodom, 

 described by ancient writers as fruits fair to the view, but 

 crumbling into dust when handled. A late writer,* how- 

 ever, has shown that these tempting and deceptive produc- 

 tions are the real fruits of a tree, the Asclepias procera, 

 resembling our common silk-weed in its botanical characters. 



Clusters of three or four round and smooth galls are 

 often seen on the small twigs of the white oak. They are 

 nearly as large as bullets, of a greenish color on one side, 

 and red on the other. They approach in hardness to the 

 Aleppo galls, and perhaps might be put to the same use. 

 Each one is the nest of a single insect, which turns to a fly 

 and eats its way out in June and July, having passed the 

 winter as a chrysalis, within the gall, lodged in a clay-col- 

 ored egg-shaped case, about three twentieths of an inch 

 long, and with a brittle shell. These httle cases appear 

 to be cocoons, but are not made of silk or fibrous matter. 

 Similar cocoons are found within many other galls, and I 

 have some which were discovered under stones, and were 

 not contained in galls, but produced gall-flies, the insects 

 having left their galls, to finish their transformations in 

 the ground. The gall-fly of the white oak varies in color. 

 Sometimes it closely resembles the gall-fly of our oak-apple, 

 differing from it only in size, and in wanting the brownish 

 spot and dark-colored veins on the fore wings; and some- 

 times it is of a dull brownish-yellow color, with a brown 



* Kobinson's Biblical Researches in Palestine, Vol. II. p. 235. 



