188 



KNOWLEDGE. 



[October 2. 1808. 



crevice of the bark, and there lays her single egg, which is 

 large enough to occupy the whole of the cavity of her body. 

 Having done this, she, or rather all that is left of her, at 

 once dies, though she may, as we have said above, die even 

 without depositing her bui-den, leaving it enshrouded in 

 her withered skin. Thus, after having passed through a 

 pedigree of seven successive generations of beings, we find 

 ourselves back again at the stage with which the cycle 

 commenced. The eggs he on the trees throughout the 

 winter, and next season the same series is gone through 

 a^ain. From a history such as this, it follows of course 

 that by far the greater number of aphides seen during 

 any particular summer do not originate fi-om eggs at all, 

 and that indeed, when compared with the number of living 

 beings produced altogether, the total number of eggs is 

 ridiculously small. 



Now it is evident fi'om the above that galls which are 

 produced by insects of this sort differ in many respects 

 fi-om those which have previously occupied our attention. 

 In the first place they are not associated with their 

 fabricators throughout the whole cycle of their varied 

 existence, but only during certahi stages. Again, it is 

 not the true female of the species, but the stem-mother, 

 that originates these aphis-galls, and they are used by her 

 and her immediate progeny till the migrating stage is 

 reached. Moreover, the original puncture which started 

 the gall is not made, as has always been the case hitherto, 

 for the lodgment of an egg, but simply for the obtaining 

 of food. In fact, no egg is ever associated with the gall 

 at all. The galls produced by the different species are of 

 various shapes and sizes, and as they shelter communities, 

 not individuals, their size bears no relation to that of the 

 individual aphides ; some are as large as hazel nuts, and 

 some occasionlly reach the size of a ripe fig. They are 

 found frequently on the stalks of leaves, as in Fig. 12, 



which shows one commonly 

 found on the stalks of poplar 

 leaves ; sometimes they rise 

 from the blade of the leaf 

 itself. They are hollow, and 

 have an opening at the end, 

 , out of which the winged 

 }y " emigrants " escape. If 

 y \ opened they are found to con- 

 /' ,' tain not only a company of 

 / aphides, but a globule of 

 sweetish liquid as well, and 

 a quantity of a white mealy 

 powder, with which also the 

 bodies of the insects are 

 dusted. The nature of the 

 liquid and its exact relation 

 to the inhabitants of the 

 gall is doubtful ; it is often 

 too large in amount for 

 there to be a possibility of 

 its being entirely a secre- 

 tion by the insects, and some 

 naturalists suppose it to be 

 in part at least exuded sap, 

 whicJi has escaped through 

 the many punctures inflicted 

 by the aphides upon the 

 walls of the gall. The mealy 

 powder clings to the surface of the globule, and thus 

 prevents it from injuring the delicate insects amongst 

 which it lies. According to Dr. M. C. Cooke, liquid of this 

 sort found in large elm-galls is collected in France and used, 

 under the name of " elm-water," as a lotion for sore eyes. 



FlO. 12. — Aphis Gall on stalk 

 of poplar loaf, e, Hole for 

 exit of aphides. 



Fig. 13.— Gall of 

 Chermes abieti.i, 

 niiniicking fir-coues. 

 Magnified two dia- 

 meters. 



Nothing more beautiful can be imagined in the way of 

 galls than those made on the spruce, fir, and larch by 

 aphides belonging to the genus C/unncs (Fig. 13). They 

 closely mimic fir-cones, so closely in 

 fact that a section needs to be made 

 before one can be convinced that they 

 are not a legitimate fruit of the trees. 

 They are, of course, smaller than the 

 actual cones, and this would help to 

 distinguish them, were it not that 

 they are so strongly suggestive of 

 young cones. The life-history of the 

 creatures is less intricate than that 

 detailed above, and only a few points 

 need be noticed. The mother of the 

 tribe starts the gall, but she does not 

 produce li\'ing young. She lays a 

 number of eggs, which are attached to the tree imme- 

 diately around her body, each by a thread-like stalk. 

 The larvie hatched from these by their punctures 

 increase the growth of the gall, and cause the adjacent 

 leaves to swell so much as to meet one another at 

 certain spots and enclose the insects within cavities. 

 In this way a many-celled structure is built up, which 

 externally resembles a miniature fir-cone. As time 

 advances, the cone dries up, and its component scales then 

 open out so as to leave free exit for the contained insects. 

 Only one other instance of gall-growth need now be 

 referred to, and with it we revert to the type which 

 formed our earlier illustrations, viz., gall-formation on the 

 insertion of an egg. But though the type of gall is 

 similar to those formerly described, the insect cause is 

 totally different, belonging to an order we have not yet 

 had occasion to mention, viz., the Coleoptera, or beetles. 

 It is an agricultural pest, known as the cabbage gall 

 weevil. This insect is a stumpy, hard-skinned, black- 

 bodied beetle, with a long, slender, curved beak, halfway 

 down which are inserted the elbowed antennii3. The 

 mouth is at the tip of the beak, and here are situated a 

 minute pair of jaws, with which the little pest can pierce 

 the skin of a cabbage-stalk. The beetle is by no means a 

 large one, being only about one-eighth of an inch long from 

 tip of beak to end of body. When it is alarmed it tucks 

 its beak under its body, which is slightly grooved for its 

 reception, and folds its legs up closely, so that its size 

 seems much reduced, and it resembles a little lump of dirt. 

 The female insect with her beak pierces that part of the 

 cabbage stem which is below ground, and lays an egg in 

 the hole. Many such holes may be formed by the same 

 beetle near together on the same stem. A gall soon 

 forms roimd each puncture, and sometimes quite a cluster 

 of rounded knobs may be seen on the stem. The egg 

 hatching produces a footless maggot, which lives on the 

 material of the gall. When it is full grown it gnaws its 

 way through the rind of the gall and works itself iuto the 

 earth, where it fashions a little cell in which it turns to a 

 chrysalis ; this becomes a perfect beetle the next season. 

 In all its stages it is a very hardy insect, being able to 

 endure a good deal of interference with its comfort without 

 evil consequences. It will even survive being frozen stiff 

 when in the pupal condition. Though these galls are 

 small, they may become harmful by exhausting the plant, 

 when present in great numbers. Not only the cabbage 

 crop, but turnips also are subject to their attacks, though 

 they seem less injurious in this case. This little beetle, 

 which, if allowed to multiply too greatly might become a 

 serious pest, has had bestowed upon it a name by no 

 means commensurate with its diminutive size, for in our 

 cabinets it stands ticketed Ceutlior/n/nchus sulcicuUin. 



