Homes Without Hands: Being a Description of the Habitations of Animals, Classed According to Their Principle of Construction

In the right-hand upper corner of the illustration is seen a gall of some size, and nearly spherical. This is the celebrated DEAD SEA APPLE, of which such strange stories have been told.

This so-called fruit was said to be lovely and beautiful to the eye, but, instead of containing sweet juice, to be filled with bitter ashes, which filled the mouth as soon as it was bitten. Of course, the ashes were supposed to be drawn by the tree from the sunken remnants of the three evil cities beneath the bituminous waves of the Dead Sea, and to present tangible evidence of their existence.

This story, which was implicitly believed for many centuries, was at length as decidedly discredited, and the whole narrative of the ash-filled fruit denounced as a mere fable. However, recent researches have proved, as is often the case, that the main facts of the story are true, though the inference to be derived from them has been entirely mistaken. In the first place, these seeming fruits are not produced by any of those trees which are known to gardeners as fruit-bearers, but are found only upon a species of oak, which is, in fact, the same tree that furnishes the ink galls of commerce. At the proper season of the year, the oaks, which are of low stature, and more like scrubby bushes than the stately trees which are suggested by the name of oak, are seen to be covered with round, fruit-looking objects, beautifully colored, and closely resembling ripe apples. If, however, they are cut open, they will be found to be the habitation of a species of gall-fly, which has been named by Mr. Westwood Cynips insana.

It is evident that if any one were to bite a gall, especially one that was produced from the oak, the exceedingly astringent properties of the excrescence would produce a very rough and ash-like sensation to the palate, which would be increased by the dryness of its substance. Except in size, they much resemble the gall of commerce, and many persons have thought that they are produced by the same insect. These galls are also known as Mala Sodomitica, and Mad Apples, the latter term being the origin of the specific title "insana," applied by Mr. Westwood to the insect.

IMMEDIATELY below the Dead Sea Apple, and in the right-hand lower corner, may be seen two remarkable objects, which would scarcely be recognized as galls except by an experienced eye. They are, however, the production of an insect called by entomologists Cynips polycera.

These galls are found in many parts of Germany upon the oak-tree, and are at once recognized by their remarkable form. As may be seen by reference to the illustration, they are shaped something like miniature sugar-loaves, and stand boldly from the branch with their broad end uppermost. The body of the gall is slightly conical, so that, if cut transversely, it would present a circular section. The end, however, is constructed after a peculiar fashion.

It is nearly flat, "abruptly truncated" according to scientific language, and throws out several projections like horns or spines. The reader will remember that the ink gall also possesses short and sharp projections, but they start from all parts of the surface, whereas in the present species they belong wholly to the flattened end. Their number is variable, so that the end of the gall is sometimes triangular and sometimes squared, besides assuming other forms according to the number of projections. This remarkable form has earned for the insect the name of Polycera, this term being derived from two Greek words which signify "many-horned." The insect which forms this curious gall is about half as large as Cynips Kollari.

THE last example which is represented in the illustration is also found in Germany upon the oak, and is made by an insect which is called Cynips Hungarica.

This gall is represented of the natural size, whereas all the others are much diminished, in order to be inserted in so limited a space. It is a very remarkable object, and can not be mistaken for any other species. Its surface is traversed by a variable number of irregular ridges, which all radiate from the stem, and so pass longitudinally over the gall. The whole of the ridges are rough and sharp-edged, but at intervals they shoot out into hard-pointed horns, much like those which arm the preceding species. Indeed, the whole substance of the gall is remarkable for its hard texture, for, when cut with a knife, it offers as stubborn a resistance as if it were seasoned oak or elm.

That a hymenopterous insect should be able to bore its way through so hard a substance, and to make a tunnel barely wide enough for the passage of its body, and nearly three quarters of an inch in length, is really surprising. The insect is not a large one, and resembles Cynips Kollari so closely that an inexperienced observer would certainly mistake it for that insect, the distinctions being so trifling that they can only be detected by means of the microscope.

CHAPTER XXVI.

PARASITIC NESTS—(Continued).

The Oak-tree, and its Aptitude for nourishing Galls.—Compound Galls, or one Gall within another.—The Sensitive Gall of Carolina.—The Fungus of Wine-vaults.—Galls and the Insects which caused them.—Colors of Galls.—Whence derived.—The Galls of various Trees and Plants.—The Cynips parasitic upon an Insect.—Galls produced by other Insects.—Mr. Rennie's Account of the Beetle Gall of the Hawthorn.—The Beetle Gall of the Thistle.—Dipterous Gall-makers.—Leaf-miners and Galls.—Size of the Larvæ of Leaf-miners.—The perfect Insects and their Beauty.—Method of displaying the Insect.—Social Leaf-miners.—Dipterous Leaf-miners.—Animal Galls.—The Chigoe and its Habits.—Its curious Egg-sac.—Difficulty of extirpating it.—The Penalty of Negligence.—The Breeze Flies and their Habitations.—Wurbles and their Origin.—Their influence upon Cattle.—The Clerus and its Ravages among the Hives.—The Drilus, its remarkable Form, and the difference between the Sexes.—The curious Habitation which it makes.

THE reader can not but notice the singular aptitude possessed by the oak-tree for nourishing galls. No part of the tree seems to escape the presence of a gall of some sort, diverting its vital powers into other channels. The tree, however, does not appear to suffer from them, and it is just possible that they may be useful to it. The leaves are studded with galls, and so are their stems. The branches are covered with galls of various shapes, sizes, and colors, some bright, smooth, and softly colored, like ripe fruit, others hard, harsh, spiny, and rough, as if the very essence of the gnarled branches had been concentrated in them. There are galls upon the flowers, galls upon the trunk, and even galls upon the root.

Some oak-galls may be called compound galls. M. Bosc mentions a small gall which is found upon the American oak. It is not larger than a pea, and if shaken is found to contain some hard substance loosely lodged in its interior. When the gall is cut open, a very curious state of things is seen. The walls are very thin, so that, in spite of the small dimensions, the cell is larger than that of many Cynipidæ. Within the cell no insect is discovered, but in its place a little spherical object, about as large as a No. 5 shot, which is very hard, and rolls about freely in the interior. If this be opened, the larva is found within it, reminding the adept in fairy lore of the white cat whose gifts were inclosed in a succession of nuts, each within the other. How these singular little cellules are made is not known, though their discoverer expended great trouble and patience upon them.

The same naturalist mentions another species of gall, also found upon the oak in Carolina. It is spherical, covered with prickles like a thistle, and beset with a thick downy covering of rather long hair. Many other galls possess these characteristics, but the most curious point connected with this species is that the hairs are as mobile as those of the sensitive plant, and, as soon as they are touched, sink down, and never afterward regain their former position.

There is a kind of fungus which is found in wine-vaults, and which exhibits a similar phenomenon. When newly grown it hangs in great masses, like tufts of pure cotton wool. But to carry a specimen away is impossible, for, as soon as it is touched, it begins to contract, and in a minute or two shrivels up into a flat membranous mass, that looks like the web of the house-spider. M. Bosc was unable to rear any of the inmates of these galls.

THE size of a gall is no criterion of the dimensions or numbers of the insect which made it. Even in the galls which infest the oak, the smallest galls often furnish the largest insects, and in some specimens brought from Greece, the gall is as large as an ordinary black currant, while the cell would contain a red currant, showing that the inhabitant of the cell must be a large one in order to fill it. Again, although the oak apple and rose bedeguar do contain a great number of insects, there are many examples where galls scarcely as large as a pea contain from ten to fifteen insects, while the ink gall and the large Hungarian gall are inhabited by a single insect.

One of the most curious problems is, to my mind, that of the brilliant colors with which many of these galls are decorated. That the rose bedeguar should be so beautifully adorned with scarlet and green is a fact which does not seem to excite any astonishment, inasmuch as it may be said that the colors which ought to have been developed in the petals and the leaves have been diverted from their proper course, and forced to exhibit themselves in the gall.

Botanists and physiologists will see that this idea is quite groundless, but to the uninstructed and popular mind it has a sort of plausibility, that often commands assent. But when we come to the oak-tree the case is at once altered, and some other cause must be found for the lovely colors of its galls. The cherry galls are as brightly colored as any apple, and the soft hues of the oak apple are nearly as beautiful, though not so brilliant. Yet the oak possesses no such store-house of color as is popularly attributed to the rose. Its leaves are simple green, and its flowerets are so colorless as scarcely to be distinguished by the unassisted eye.

Whence, then, are derived these beautiful colors? Some hasty observers, who have neglected the first rule of logic, and drawn a universal conclusion from particular premises, have said that the colors of the gall are derived from the insect, adducing as a proof of their assertion the brilliant colors which equally deck the rose bedeguar and the Cynips rosæ from which it sprang. But if they had only followed the example of careful naturalists, who, like Dr. Hammerschmidt, have examined and drawn between two and three hundred species of galls, so hasty a generalization would never have been made. The cherry or leaf gall of the oak is every whit as gorgeously colored as the bedeguar of the rose, while the insect that made it is quite black. It is true that the diaphanous wings glitter as if they were made of polished gems; but this appearance is due, not to the wings themselves, but to the myriad hairs with which they are regularly studded, each hair acting as a miniature prism by which the light is refracted and broken into the resplendent hues of the rainbow.