The anthophilous insects do not visit all flowers indifferently. In the conrse of an entomological excursion in which I had as a companion the very learned Professor Giard, we made a large collection of Micropteryx calthella in the suburbs of l'Isle Adam. The resplendent country offered to the honey-collectors the most diverse corollas, but the graceful little moth had chosen for its exclusive use the yellow cupule of the buttercup (bouton d'or), Ranunculus acris. This was not an accidental phenomenon. In his treatise on 1 1 Floral Biology, ' ' which is a compendium of the relations noted between insects and flowers, Paul Knuth noticed our Micropteryx upon another Ranunculus (R. repens), but the list is not complete, for the species frequents also the great Ranunculus of the marshes (CaltJia palustris), which really has given it its name. In fact, Micropteryx calthella frequents the flowers of several RanunculaceaB with yellow flowers, and it is probably by mistake that Stainton has recorded it upon flowers of Carex.
We have here, then, a species which limits itself to a very small number of flowers,-indeed, to flowers of the same coloration and of the same type. Insects of this kind are rather rare. According to Kerner (1891), Bombus gerstaeckeri devotes its attention to the aconites, Andrena florea to the bryonias, Osmia adunca and 0. loti to the vipérines. This exclusivism is not, however, without elasticity. Osmia papaveris lines its nest always with the red petals of the poppy, but in Cerdagne, where this flower is entirely lacking, Ferton has seen the insect choose the petals of another flower, the musk mallow. Analogous variations will, without doubt, be observed with many insects which have a choice of flowers without being narrowly adapted to them. When, on the other hand, a species has suffered a great disaster through its adaptation to special plants, it can no longer frequent others. So it is that the Hymen-optera of the genus Blastophaga exclusively frequent figs whose fertilization they assure. It is so, also according to Riley, that the American moths of the genus Pronuba are closely adapted to the yuccas and can fertilize the flowers of these plants only. But in general anthophilous insects are strongly eclectic and get their nourishment from the most diverse plants. With the nocturnal Sphingid, which limit themselves to a small number of flowers, and the day sphinx (Macroglossa stellatarum),which has no especial choice among the corollas, the species of Micropteryx, and our charming noctuids of the genus Plusia, with the bumblebees and with our honey-bee, we cannot perceive any great specialization from this point of view.
However, it is not by chance that we can collect these very eclectic speciesi In their excellent treatise on apiculture, Gaston Bonnier and G. de Layens observed that the collecting-flight of the honey-bees is always appropriate to the weather and the place. Each morning the colony sends out into the country scouts which explore the neighborhood to find out the best plants and the proper places for collecting honey. On the return of this advance-guard the workers go out in clouds, some charged with the collection of pollen, the others to sip the honey, as Aristotle has already pointed out. The principle of the division of labor is perfectly observed, each collector gathering exclusively the one or the other product, and almost always, at least in each journey, limiting its visits to a single kind of flower. The harvest varies according to the seasons, and in each season certain flowers are the object of their preference, among others sainfoin, honey-locust, clover, which furnish an abundance of preferred nectar. The beekeepers know this faculty of choice very well, and have profited by the knowledge by growing near the colonies an American plant, the Phacelia of California, which flowers luxuriantly for a long time.
Even with the most eclectic flower-loving insects the choice of flowers is always limited, for most of them are primarily fond of nectar and many of them possess no organ which will enable them to reach into all corollas. Gaston Bonnier1 has justly said that the true anthophiles "go in the greatest number where the nectar is . . . the easiest to collect." And when, in his memorable study upon the Alpenblumen (Alpine flowers), Herman Miiller divided the flowers into nine groups according to the relation which they bear to anthophilous insects, he had only to arrange the preceding observation in systematic form. His system has been held in great favor. It serves as a basis for the great "Treatise on Floral Biology" by Paul Knuth and has recently been popularized by Kirchner (1911). However, if it is beyond criticism in its principles, it bares its flank by its complexity and above all by the ambiguous delimitation of its groups. So if flowers are especially frequented, some by Lepidoptera, others by Hymenoptera, certain others by Diptera, it does not follow that they are suitable for little insects, and most of the anthophiles go to the flowers in which the pollen is largely exposed, upon those where the nectar is half hidden (Ranunculace) and upon the Scabiosa and the composites in which the nectar occupies the bottom of the corollary tube. The conclusion from this study is that the length of the beak forces the insects to a selection of flowers for the collection of nectar. With their beak seven or eight millimeters long, our particular little Lycsenas are not able to reach down as deeply as Papilio machaon, with which the organ may reach a length of fifteen millimeters. These differences are still greater with the Sphingid. In Smerinthus tilice the beak measures no more than three millimeters, but with the Macroglossa which frequents the honeysuckle it reaches twenty-eight millimeters, and in the sphinx of the morning-glory eighty millimeters. Muller states that with a certain American species, Macrosilia cluen-tius, it may reach a quarter of a meter.
1 Les nectaires, 1879. (Ann. Sci. Nat. Botanique, ser. 6. v. 8).