102 



THE AMERICAN ENTOMOLOGIST. 



be, namely upou the leaf instead of upon the 

 twig, differed in no respect from those that 

 occurred upon the adjoining twig ! So definitely 

 are the form, size, color and texture of these sin- 

 gular productions determined by the insect that 

 cause the abnormal growth on the infested plant, 

 so little does it matter from what particular part 

 of the plant the abnormal growth is developed! 

 Neither does it make any difference, as a general 

 rule, if the same species of gall-making insect 

 operates upon distinct species of plants belong- 

 ing to the same botanical genus. We have col- 

 lected, for example, numeroiis instances where 

 the same Gall-fly (C(/«/^«) attacks distinct but 

 allied species of oak, and yet produces galls 

 that are entirely undistinguishable, no matter 

 upon what species of oak they occur.* 



We are all of us so familiarized with one or 

 more of the wonderful processes b)' which ani- 

 mal and vegetable organisms reproduce them- 

 selves, that it seems in no wise astonishing that 

 a sheep, for example, should generate a sheep, 

 a hone}'-bee a honey-bee, an oak an oak, and a 

 cabbage a cabbage. In all such cases, however, 

 an animal reproduces an animal, or a vegetable 

 reproduces a vegetable, and the same species, 

 whether animal or vegetable, reproduces an 

 almost exact image of itself either in the next or 

 in some subsequent generation. But in the case 

 of galls, we have the very astonishing and 

 otherwise unparalleled fact of two organisms, 

 the one animal the other vegetable, cooperating 

 together to generate a third oi-ganism, entirely 

 different in all its characters from any thing that 

 either of the two parent organisms is capable 

 by itself of producing, and just as definite and 

 invariable in shape, size, texture and color, as 

 animal and vegetable productions that belong 

 to the same species usually are. Take, for in- 

 stance, a thousand "oak-apples" (Pig. 78) 

 off black oak, and a thousand apples from 

 an apple-tree. You will find that the former 

 resemble each other, both externally and inter- 

 nally, quite as closely as do the latter. Yet to 

 produce an apple all that is required is a living 

 and growing apple-tree of sufficient age ; while 



«See Proc. Ent. Soc. PhUa. Ill, p. B39, note. Thf gall 

 resembling the oak-buUetgall (Q. globulus, Fitch) whio. is 

 there raeotioned as occurring on Burr oak, has been since 

 ascertained by us to be produced by a distinct species of 

 Gall-fly from that which produces the" oak-bullet gall. The 

 gall itself has the same very remarkable internal structure, 

 fjut diffens externally in being somewhat rougher and in 

 nsually having a little nipple at its tip, whence we may call 

 it the oak-nipple gall (Q, mamma) . The fly, like that of the 

 oak-bullet gall, occurs only in the female "seS, but is distin- 

 guishable at once from that species by having anteunie that 

 are shorter, stouter,' and 13-jointed instead of H-jointed. It 

 is also, on the average, about one-third larger, and has the tip 

 of the ventral valve in a somewhat obtuse, instead of in a 

 somewhat acute angle, but in other respects agrees very 

 closely . Thirty-eight spccirilcns , all females , came out from 

 galls of the same year's growth Oct. 22 to Nov. 7. Ifmay 

 he called Cynips q mrtmma, as it is an midescribed species. 



to produce an " oak-apple" there is necessarily 

 required the joint co-operation of a gall-fly and 

 an oak, the first an animal, the second a veget- 

 able organism: and if either the gall-fly or the 

 oak were swept out of existence to-morrow, the 

 oak-apple that they unite to produce would at 

 the very same time cease to exist in this world. 



The insects wliich are known to be the archi- 

 tects of galls are by no meaus an isolated groui), 

 but belong to several different Families in no 

 less than five dift'erent Orders. They may be 

 enumerated as follows : The Snout-beetles and 

 the Long-horned Beetles {Coleoptera) , the Saw- 

 flies and the Gall-flies {Hynienoptera), the 

 Tinea and Tortrix Families (Lepidoptera), the 

 Flea-lice (Psylla). Plant-lice and Bark-lice (IIo- 

 moptera), and the Gall-gnats and certain groups 

 belonging to the great Musca Family {Dip>tera'). 

 Ill none of these Families is the gall-making 

 faculty universal, and in not many of them is it 

 general, but is on the contrary confined to par- 

 ticular species, the very same genus often con- 

 taining certain species that make galls and cer- 

 tain others that do not.* Besides the above 

 gall-making Families, all of which are true 

 Insects, many of the Mites {Acarus family), 

 which are not true Insects, construct npon vari- 

 ous trees galls of no very conspicuous size, 

 shape or structure. (See Amek. Entom., p. 57). 



Galls originate iu two distinct modes, either 

 first, by the motlier insect depositing one or 

 more eggs in or on the part of the plant which 

 she attacks, or second, by a young larva station- 

 ing itself upon a leaf or other part of a plant, 

 and irritating its surface with the organs of its 

 mouth, until a hollow is gradually formed which 

 eventually becomes a more or less tighth' closed 

 sack, inside which the larva develops to matur- 

 ity and propagates its species. In this latter 

 case, which is peculiar to the Plant-lice, the 

 Bai"k-lice and the Mites, young larva; born 

 within the gall frequently stray away through 

 the partially open mouth of the enclosing sack, 

 and found new galls the same season either 

 upon the same or upon adjoining leaves. This is 

 the rule with gall-making Bark-lice and Mites. 

 But in galls made by Plant-lice, the entire brood 

 of larv» reared within the gall remain therein 

 till they have most of them reached maturity 

 and acquired wings. The gall then, by a beau- 

 tiful provision of nature, gapes open to allow of 

 their escape, usually at the mouth of the sack 

 formed by the mother insect, but iu certain 

 cases in some other part of the sack. 



It will thus be seen that this second mode of 



•As, for example, the geuus Nematud among the .Saw-flies 

 and the genus Cecidomyia among the Gall-gnats, 



