THE AMERICAN ENTOMOLOGIST. 



73 



lowing spring or summer; but on this matter we 

 can at present only judge from analogy. We may 

 add that we are acquainted with an undescribed 

 Ilackberry-gall, formed by a gall-gnat, where 

 the cells drop to the ground when mature pre- 

 cisely as in this gall which is formed by a Gall- 

 fly. 



So rapid is the development of the Leafy 

 Oak-gall, from the time when it first begins to 

 appear to the time when the cells that contain 

 the larva drop to the ground, that up to 18G9 

 we had never seen anything but the empty gall. 

 We have ourselves met with it in Northern Illi- 

 nois both on Bur Oak and on White Oak ; and 

 Mr. Bassett of Waterbury, Conn., found it upon 

 the Chinquapin Oak (<?. ^jmio/rfe,?). We have 

 also received specimens from Mr. McAfee of 

 Freeport iu North Illinois, and others from B. 

 H. Brodnox of Pickens' Station, Miss.; so that 

 it would seem to be pretty generally distributed 

 throughout the Union. Oak-bushes that have 

 been badly infested by this gall present a sin- 

 gular appearance iu tiie following winter and 

 spring; the empty galls turning black, losing 

 tlio tips of many of their leaves, and looking 

 then more like an army of great hairy black 

 caterpillars, curled up in repose all over the 

 naked twigs, than anything else to which we 

 can compare them. In 1866, from ignorance of 

 the true history of this gall, speaking of it as 

 the Oak-cabbage gall {Q. brassica, Walsh MS.), 

 we erroneously assumed it to be the work of 

 some unknown Gall-gnat, many species of which 

 group of insects originate galls on different kinds 

 of oak.* At that period we had bred from it 

 nine specimens of a Guest-sawfly {Nematus 

 quercicola, Walsh), which like certain other 

 guest-flies is remarkable for being to all exter- 

 nal appearance absolutely undistinguishable 

 from a true gall-making insect {Nematus s. jn- 

 sum, Walsh), that produces a leaf-gall on a spe- 

 cies of Willow. And yet, though externally 

 undistinguishable, these two Saw-flies differ 

 notably in their habits, the Gall-maker always 

 leaving its gall and going underground to pass 

 into the pupa state, and the Guest-fly remaining 

 in the Leafy Oak-gall all through the winter, 

 and not coming out in the fly state till May or 

 June of the following year. So little depen- 

 dence can we place upon the decisions of mere 

 closet-naturalists, relative to the identity or dis- 

 tinctness of species ! For in this, as in several 

 other such cases enumerated by us, it is impos- 

 sible for any one to tell the difference between 

 the Gall-maker and the Guest-fly; and yet it 



•See a Paper on Willow Galls in Proc. Enl . Soc. Phil. VI. 



would be as absurd to suppose that the two 

 form but one species, and that one and the same 

 species is sometimes the architect of its own gall 

 and sometimes spungos upon true gall-making 

 insects for a nidus for its future offspring, as it 

 would be to imagine that the European Cuckoo, 

 or our North American Cowbird, sometimes 

 builds a nest for itself and sometimes surrepti- 

 tiously deposits its eggs in the nests of other 

 birds. 



The Lygodesmia Pea-gall. 



(Lijgodesmice pisum, new species.) 



There is a rush-like plant about a foot high, 

 with slender sprangllng stems and a few rigid 

 lance-shaped leaves, which inhabits Nebraska 

 and the regions to the east and north of that 

 territory, and is known to botanists as Lygo- 

 desmia juncea. On the stems of this plant there 

 often grows a profusion of round or oval pea- 

 like galls, ranging in diameter from } to 4 an 

 inch, such as are represented in the annexed 

 Figure 47. In the autumn each of these galls 

 contains, in a central cavity about 

 one-tenth of an inch in diameter, a 

 fat yellow legless maggot, with a 

 large round head and robust jaws 

 tipped with black. Except the cen- 

 tral cell, the rest of the gall consists 

 of a dense whitish spongy matter, 

 which ultimately becomes so hard 

 as to be penetrated with some difli- 

 culty by the thumb-nail. About the 

 middle of the following May there 

 eats its way out of the gall, through 

 a small pin-hole (Fig. 47, a), a 

 black Gall-fly about one-eighth of 

 an inch long, which scarcely dif- 

 fers in general appearance from 

 the Oak-plum Gall-fly (Vol. I. j). 

 Coi„rlopaque 1^4, Fig. 81) except "ill being so 

 a^ll-gl■ay. much smaller and in lacking the 

 dark shade on the front wings. This Gall-fly is 

 entirely new to science, and, as we have already 

 explained, it is especially interesting because— 

 growing as it does on a group of plants not 

 hitherto known to be infested by Gall-flies— it 

 presents structural characters difl'erent from 

 those found in any other Gall-fly. In otlicr 

 words, a new genus has to be established to 

 receive it, besides giving the characters separ- 

 ating it from any other species belonging to the 

 same genus, which may hereafter be discovered. 

 But as such details as these are only of interest 

 to the scientific reader, we shall throw them 



