lar reason the males of any species of bee may not visit the same flowers as the females, though the attraction of the female may largely influence their course, in which respect they exhibit quite human sentiments. It would, of course, be in vain to look for the males of Bombus and Halictus on the flowers of spring, since they do not appear until mid-summer. In the case of diœcious plants, or plants in which the sexes are on different individuals, the bees visiting the staminate flowers are more numerous and are sometimes widely different from those visiting the pistillate. The common sumach is a good example. Indeed the bees visiting a flower in its early stages may differ from those visiting it in its later stages. Again the visitors to a flower may differ, both in number and kind, in different seasons.
The depth at which the nectar is concealed is another most important factor in controlling the visits of bees. In some flowers it is fully exposed on a flat surface where it is accessible to all insects; in others it is at the bottom of a slender tube, where it can be reached only by the larger moths. The familiar fable of the crane and the fox is constantly illustrated among flowers. As a matter of fact, bumblebees and butterflies avoid rotate, flat flowers containing little nectar, since their long tongues do not permit them to suck easily on such a surface. On the other hand, it would be useless to look for the smaller bees with short tongues on the larkspurs and clovers, for the nectar is quite beyond their reach.
As we take our leave of the oligotropic bees it may be inquired if there are any other insects, which visit only one species of flower. There are many others, especially among butterflies and moths. The flag beetle (Mononychus vulpeculus) passes its entire life on the blue flag (Iris versicolor). This small weevil feeds both on the pollen and nectar and sometimes gnaws the flower-leaves badly. The eggs are laid in the young seed capsules, where the larvæ feed on the ripening seeds. Both the adult beetles and larvæ are supported at the expense of the blue flag. The legitimate pollinators are bees and while the flag beetle may rarely effect pollination it does far more harm than good. This symbiotic relation is a benefit to the insect, but anto the plant.
Two slender metallic-hued beetles (Donacia rufa and Donacia piscatrix) find very comfortable quarters within the flowers of the yellow water lily, where they idle away much time drinking nectar and eating pollen. They lay their eggs on the leaves and the larvæ burrow in the stems. As in the case of the flag beetle this arrangement is evidently more to the advantage of the beetles than of the plants.
The night-blooming yucca, or Spanish bayonet, which flourishes throughout the southern states, is pollinated exclusively by a small nocturnal moth. The larvæ of the moth live in the seed-capsules. Thus both plant and moth are reciprocally dependent on each other, and the destruction of the one would be followed by the disappearance of the other. But in most instances the insect receives the greater benefit.