Imagens das páginas

ever has a whorl of gay petals; and though the converse is not quite true, yet almost all insect-fertilized plants are noticeable for their brilliant tints of red, white, blue, or yellow. The structures in which these pigments reside have no function whatsoever, except that of attracting the insect eye. They are produced by the plant at an enormous physiological expense; and if their object were not to secure the visits of insects, they would be just so much dead loss to the species. Nor is it only once that these colored corollas have been developed. They occur, quite independently, in both great divisions of flowering plants, the monocotyledons and the dicotyledons. This coincidence could hardly have happened had it not been for that original tendency which we already noticed for pink, scarlet, or orange pigments to appear in the neighborhood of the floral organs. Nor is it twice only, in all probability, that flowers have acquired bright petals through insect visits, but a thousand times over. In almost every family, insect-fertilized, self-fertilized, and wind-fertilized species are found side by side, the one with brilliant petals, the others with small, green, and inconspicuous flowers. For comparison with the dog-rose, one could not find a better type than that common little early spring blossom, the dog's mercury. It is a wind fertilized flower, and it does not wish to be seen of insects. Now, this mercury is a very instructive example of a degenerate green flower. For, apparently, it is descended from an insect-fertilized ancestor with bright petals; but owing to some special cause, it has taken once more to the old wasteful habit of tossing its pollen to the wandering winds. As a consequence it has lost the bright corolla, and now retains only three green and unnoticeable perianth-pieces, no doubt the representatives of its original calyx. Almost equally instructive is the case of the groundsel, though in this case the process of degradation has not gone quite so far. Groundsel is a degenerate composite, far gone on the way of self-fertilization. No class of flowers have been more highly modified to suit the visits of insects than the composites. Hundreds of their tubular bells have been crowded on to a single head,

so as to make the greatest possible attractive display; and in many cases the outer blossoms of the head, as in the common yellow ragwort, or in the daisy and the sunflower, have been flattened out into long rays, which serve as pennants or banners to catch the insect eye.. They are very sucessful flowers, perhaps the most successful family on the whole earth. But the groundsel, for some reason of its own, has reversed the general family policy. It is rarely visited by insects, and has, therefore, apparently taken once more to self-fertilization; and a complete alteration has thus been effected in its appearance, when compared with its sister composites. Though it has not yet quite lost its yellow centre blossoms, it has no rays, and its bells are almost concealed by its large and ugly green involucre. Altogether, we may say that groundsel is a composite. far advanced on its way to a complete loss of the characteristic composite habits. It still receives the visits of a very few stray insects; but it does not lay itself out to court them, and it is, probably, gradually losing more and more of its winged clients from day to day. Thus we see that any flower which will benefit by insect-fertilization, whether it be a monocotyledon or a dicotyledon, high up or low down in either series, is almost sure to acquire brilliant petals; while, on the other hand, any flower which gives up the habit of relying upon insects is almost sure to lose or minimize its petals once more, and return to a state resembling in general type the catkins and grasses or the still lowlier self-fertilized types.

The same sort of conclusion is forced upon us if we look at the various organs in each flower which display the brilliant pigments. The petals are most commonly the seat of the attractive coloration, as in the dog-rose and the marshmallow. But in many other flowers, like the fuchsia, the calyx is also beautifully colored, so as to aid in the general display. In the tulips and other lilies, the crocus, the iris, and the daffodil, sepals and petals are all colored alike. In marvel-of-Peru and purple clematis, the petals are wholly wanting. In the common meadow-rue, it is the essential floral organs themselves which act as allurements; while, in the mesembryan.

themums, the outer stamens become flattened and petal-like, so as to resemble the corolla of other flowers. In the .composites, like daisies, where many blossoms are crowded on one head, the outer row of blossoms are often similarly flattened into rays which only serve the purpose of attracting insects toward the fertile flowers of the centre. Nor does the coloring process stop at the regular parts of the flower alone; the neighboring bracts and leaves are often even more beautifully tinted than the flowers themselves. In the great white arums, grown in windows as Ethiopian lilies, the actual blossoms lie right inside the big sheath or spathe, and cluster round the tall yellow spike or spadix in the centre; and this sheath acts the part of petals in the more ordinary flowers. Many euphorbias have very inconspicuous little blossoms, but each small colony is surrounded by a scarlet involucre which makes them some of the gayest among our hot-house plants. The poinsettia, which is so familiar a fashionable dinner table plant, bears little yellow flowers which would not of themselves attract the eyes of insects; but it makes up for this deficiency by a large surrounding bunch of the richest crimson leaves, whose gorgeous coloring makes the tree a universal favorite with tropical bees and butterflies. The lovely bougainvillea carries the same idea one step further, for its small flowers are enclosed by three regularly-arranged bracts of a delicate mauve or pink; and when one sees a tree covered with this magnificent creeper in full blossom, it forms one of the most glorious masses of color to be found in the whole of external nature. Many tropical plants, and especially those of parasitical habit, are much given to developing these extra allurements of colored leaves, and their general effect is usually one of extreme brilliancy. From all these examples, we can draw the conclusion that color does not belong by original nature to one part of the plant rather than another; but that wherever the colored juices which result from oxidation of chlorophyll and its analogues began to show themselves, in the neighborhood of the stainens and pistil, they would attract the attention of insects, and so grow more and more prominent, through natNEW SERIES.-VOL. XL. Nc. I

ural selection, from generation to generation, till they finally attained the present beauty of the tulip, the rose, the poinsettia, and the bougainvillea.


From this marvellous reaction of the color-sense in insects upon the vegetal world, we must next pass on to its reaction upon the hues of insects themselves. For we probably owe the exquisite wings of the butterfly and the gorgeous burnished bronze of the rosebeetle to the very same sense and the very same selective action which has produced the hues of the lily and the hyacinth. What proofs can be shown that the colors of insects are thus due to sexual selection? In the first place, we have the certain fact that bees at least, and probably other insects, do distinguish and remember colors. Not only so, but their tendency to follow color has been strong enough to produce all the beautiful blossoms of our fields and gardens. Moreover, we have seen that while bees, which are flower-haunters, are guided greatly by color, wasps, which are omnivorous, are guided to a less extent, and ants, which are very miscellaneous feeders, not at all. may be objected that insects do not care for the color apart from the amount of honey; but Mr. Anderson noticed that when the corollas of certain flowers had been cut away, the insects never discovered or visited the flowers; and Mr. Darwin lopped off the big lower petals of several lobelia blossoms, and found that the bees never noticed them, though they constantly visited the neighboring flowers. On the other hand, many bright-colored bells have no honey, but merely make a great show for nothing, and so deceive insects into paying them a call on the delusive expectation that they will be asked to stay to dinner. Some very unprincipled flowers, like the huge Sumatran rafflesia, thus take in the carrion flies, by resembling in smell and appearance a piece of decaying meat. Moreover, certain insects show a preference for certain special flowers over others. One may watch for hours the visits paid by a bee or a butterfly to several dozens of one flower, say a purple lamium, in succession, passing by unnoticed the white or yellow blossoms which intervene between them. Fritz Müller mentions an inter


esting case of a lantana, which is yellow on the first day, orange on the second, and purple on the third. "This plant," he says, "is visited by various butterflies. As far as I have seen, the purple blossoms are never touched. Some species inserted their probosces both into yellow and into orange flow ers; others, as far as I have observed, exclusively into the yellow flowers of the first day.' Mr. T. D. Lilly, an American naturalist, observed that the colored petunias and morning-glories in his garden were torn to pieces by bees and butterflies in getting at the honey, while the white or pale ones were never visited. These are only a few sample cases out of hundreds, in which various observers have noted the preference shown by insects for blossoms of a special color.

Again, we may ask, Do different species of insects show different degrees of æsthetic taste? The late Dr. Hermann Müller, who specially devoted himself to the relations between insects and flowers, showed most conclusively that they do. The butterflies, which are at once the most locomotive and the most beautiful of their class, appear to require larger masses of color for their attraction than any other group; and the flowers which depend upon them for fertilization are, in consequence, exceptionally large and brilliant. Müller attributes to this cause the well-known beauty of Alpine flowers, because bees and flies are comparatively rare among the higher Alps, while butterflies, which rise to greater elevations in the air, are comparatively common; and he has shown that, in many cases, where a lowland flower is adapted for fertilization by bees, and has a small or inconspicuous blossom, its Alpine congener has been modified so as to be suited for fertilization by butterflies, and has, therefore, brilliant bunches of crimson or purple blossoms. In his last work he shows that, while bees form as many as 75 per cent of the insects visiting the beautiful and attractive composites, they form only 14 per cent of those which visit the plain green and white umbellates, like the wild carrot and fool's parsley. Butterflies frequently visit the composites, but almost never the unbellates, which last depend mainly upon

[ocr errors]

the smaller flies and other like insects. Of two small hedge flowers, Galium mollugo and G. verum, Müller notes that they agree closely in other points, but the first is white, while the second is yellow, which, he says, renders it more attractive to small beetles. Of certain other flowers, which lay themselves out to attract wasps, Müller quaintly observes that they are obviously adapted to a less æsthetically cultivated circle of acquaintances."' So that the close studies of this accurate and painstaking naturalist led him to the conclusion that insects differ greatly from one another in their taste for color. Probably we shall be right if we say that the most aesthetic among them all are the butterflies, and next the bees-these two classes having undergone the most profound modifications in adaptation to their flower-haunting life-and that the carrion flies and wasps bring up the rear.

Is there any evidence, however, that insects ever notice color in anything else but flowers? Do they in their own mates, and use it as a means of recognition? Apparently they do, for Mr. Doubleday informed Mr. Darwin that white butterflies often fly down to pieces of white paper on the ground, mistaking them doubtless for others of their species. So, too, Mr. Collingwood notes that a red butterfly, let us say, nailed to a twig, will attract other red butterflies of the same kind, or a yellow one its yellow congeners. When many butterflies of allied species inhabit the same district, it often happens that the various kinds undergo remarkable variation in their coloring so as to be readily recognizable by their own mates. Again, Mr. Patterson noticed that certain blue dragon-flies settled in numbers on the blue float of a fishing line; while two other species were attracted by shining white colors. On the whole, it seems probable that all insects possessing the color-sense, possess also a certain æsthetic taste for colors.

Indeed, it is difficult to see how it could be otherwise. Whenever an animal exercises a faculty much, the exercise comes to have pleasant feelings attached to it; and this is especially the case with all sense-organs. Creatures which live on honey love sweet things; carnivores delight in the taste


blood. Singing birds listen with interest to musical notes; and even insects will chirp in response to a chirp like their own. So, creatures which pass all their lives in the search for bright flowers must almost inevitably come to feel pleasure in the perception of brilliant colors. This is not, as so many people seem to think, a question of relative intellectual organization; it is a mere question of the presence or absence of certain sense-centres.

But it may finally be urged that even though insects recognize and admire colors in the mass, they would not notice such minute and delicate patterns as those on their own wings. Let us see what evidence we can collect on this head. First of all, insects have not only produced the petals of flowers, but also the special markings of those petals. Now these markings, as Sprengel point ed out a century since, bear a constant reference to the position of the honey, and are in fact regular honey-guides. If one examines any flower with such marks upon the petals, it will be found that they converge in the direction of the nectaries, and show the bee or butterfly whereabouts he may look for his dinner. Accordingly, they must have been developed by the gradual action of insects in fertilizing most frequently those flowers which offered them the easiest indication of where to go for food. Unless insects noticed them, nay more, noticed them closely and accurately, they could never have grown to their present definite correlation with the nectary, a correlation which, Mr. Darwin says, first convinced him of the reality of their function. "I did not realize the importance of these guiding marks," says Sir John Lubbock, "until, by experiments on bees, I saw how much time they lose if honey which is put out for them is moved even slightly from its usual place." In short, inIn short, insects, like men, are creatures of habit. How complicated these marks sometimes become, we can see in most orchids.

[ocr errors]

Again, the attention insects pay to comparatively small details of color and form is clear enough from the mimicry which sometimes occurs among them. In some instances, the mimicry is intended to deceive the eyes of higher ani

mals, such as birds or lizards, and can therefore prove nothing with regard to the senses of the insects themselves. But in a few cases the disguise is adopted for the sake of deceiving other insects; and the closeness of the resemblance may be accepted as good evidence of acute vision in the class so mimicked. Thus, several species of flies live as social parasites among the hives or nests of bees. These flies have acquired belts of color and patches of hair, closely imitating the hosts whose honey they steal; while their larvæ have even the ingratitude to devour the larvæ of the bees themselves. Of course, any fly who entered a beehive could only escape detection and condign punishment, at the hands-or rather at the stings-of its inhabitants, provided it looked so like the householders as to be mistaken by them for one of the community. So any fly which showed at first any resemblance to a bee would for a while be enabled to rob with impunity; but as time went on, the bees would begin to perceive the true nature of the intruders, and would kill all those which could be readily distinguished. Thus, only the most bee-like flies would finally survive; and the extent to which the mimicry was carried would be a rough test of the perceptive powers of the bees. Now, in these particular cases, the resemblance is so close that it would take in, not only an unpractised human observer, but even for a moment the entomologist himself. Similar instances occur among mantida and crickets.

And now let us apply these facts to the consideration of the problem before us. If those insects which especially haunt flowers are likely to have so acquired a color-sense, and a taste for colors; and if they are capable of observing minute markings, bands, or eyelike spots; then we might naturally infer that they would exhibit a preference for the most beautifully colored and variously ornamented of their own mates. Such a preference, long continued and handed down to after generations, would finally result in the development of very beautiful and varied colors among the flower-haunting species. We might expect, therefore, to find the most exquisite insects among those races which are most fully adapted to a diet

[ocr errors]

such I

of honey and pollen; and believe to be actually the case. Before proceeding further, precautions should be taken against a misconception which has already occurred in this connection. It is not meant that bright colors will be found only among flower-haunters; for it may easily happen that in a few instances other causes may conspire to produce brilliant hues. Nor is it meant that all flower-haunters are necessarily brilliant; for it may also happen that some special need of protection will occasionally keep down the production of conspicuous tints. But what is meant is that brilliant colors are found with very exceptional frequency among the specially flower-haunting ani


[ocr errors]

Butterflies are the order of insects which require the largest mass of color to attract them, and which seem to possess the highest aesthetic sensibility. It is hardly necessary to say that butterflies are also the most beautiful of all insects; and are, moreover, noticeable for the most highly developed ornamental adjuncts. Those butterflies make the best matches in their world of fashion which have the brightest crimson on their wings or the most exquisite gloss in their changeful golden scales. With us, an eligible young man is too often a young man with a handsome estate in the country, and with no other attractions mental or physical. Among insects, which have no estates, an eligible young butterfly is one with a peculiarly deep and rich orange band upon the tip of his wings. Thus the cumulative proof of the aesthetic superiority of butterflies seems well-nigh complete.

If we examine the lepidoptera or butterfly order in detail, we shall find some striking conclusions of the same sort forced upon us. The lepidoptera are divided into two great groups, the moths and the butterflies. Now, the moths fly about in the dusk or late at night; the flowers which attract them are pale, lacking in brilliancy, and, above all, destitute of honey-guides in the shape of lines or spots; and the insects themselves are generally dark and dingy in coloration. Whenever they possess any beauty of color, it takes the form of silvery scales, which reflect what little light there may be in the gray gloaming.

The butterflies, on the other hand, fly by day, and display, as we know, the most beautiful colors of all insects. Here we must once more recall that difference between the structure of the eye in nocturnal and diurnal species which Mr. Lowne has pointed out. Nor is this all. While most moths are night-fliers, there are a few tropical genera which have taken to the same open daylight existence as the butterflies. In these cases, the moths, unlike their nocturnal congeners, are clad in the most gorgeous possible mixtures of brilliant metallic colors.

Other instances of like kind occur in other orders. Thus, among the beetles, there is one family, the rose-chafers, which has been specialized for flowerhaunting; and these are conspicuous for the beauty of their coloring, including a vast number of the most brilliant exotic species. Their allies, the common cock-chafers, however, which are not specialized in the same manner, are mere black and inconspicuous insects. So among the flies; most of the omnivorous families are dull and ugly; but several of the flower-haunting tribes are adorned with brilliant colors, and live upon honey. In fact, an immense majority of the brightest insects are honey-suckers, and seem to have derived their taste for beautiful hues from the nature of the objects among which they seek their food.

There is one striking and obvious exception, however, which has doubtless already suggested itself to the minds of readers. I mean the bees. These are the most flower-loving of all insects, and yet they are comparatively plain in their coloration. We must remember, however, that the peculiar nature of the commonwealth among the social bees prevents the free action of the selective preference by which we account for the brilliancy of all other flower-haunting species. The queen or mother bee is a prisoner for life; her Majesty's domestic arrangements are all made for her by the state; she does not herself seek honey among flowers, and those bees which do so have no power of transmitting their tastes to descendants, as they live and die mere household drudges. On the other hand, the solitary bees are in many cases exquisitely colored, as we

« AnteriorContinuar »