The Behavior of the Honey Bee in Pollen Collection

by Dana Brackenridge Casteel

If the collecting bee is watched for a few moments the increase will readily be noted and the fact will be established that the accumulating mass is gradually working upward or proximally from the lower or distal edge of the corbicula and is slowly covering the floor of this receptacle. (See [fig. 8], b, c, and d.) In many instances the successive contributions remain for a time fairly separate, the whole mass being marked by furrows transverse to the long axis of the tibia.

Sladen (1912, b) notes the interesting fact that in those rather exceptional cases when a bee gathers pollen from more than one species of flowers the resulting mass within the corbicula will show a stratification parallel to the distal end, a condition which could result only from the method of loading here indicated.

As the pollen within the basket increases in amount it bulges outward, and projects downward below the lower edge of the basket. It is held in position by the long hairs which fringe the lateral sides of the basket, and its shape is largely determined by the form of these hairs and the direction in which they extend. When the basket is fully loaded the mass of pollen extends laterally on both sides of the tibia, but projects much farther on the posterior side, for on this side the bounding row of hairs extends outward, while on the anterior edge the hairs are more curved, folding upward and over the basket. As the mass increases in thickness by additions from below it is held in position by these long hairs which edge the basket. They are pushed outward and many of them become partly embedded in the pollen as it is pushed up from below. When the pollen grains are small and the whole mass is well moistened the marks made by some of the hairs will be seen on the sides of the load. (See [fig. 9], a.) These scratches are also transverse in direction and they show that the mass has been increased by additions of pollen pushed up from below.

Even a superficial examination of a heavily laden basket shows the fallacy of the supposition that the long lateral fringing hairs are used to comb out the pollen from the brushes of either the hind or middle legs by the crossing of these legs over the lateral edges of the baskets. They are far from sufficiently stiff to serve this purpose, and their position with relation to the completed load shows conclusively that they could not be used in the final stages of the loading process, for the pollen mass has completely covered many of them and its outer surface extends far beyond their ends. They serve merely to hold the pollen in place and to allow the load to project beyond the margins of the tibia.

The auricle plays a very essential part in the process of loading the basket. This structure comprises the whole of the flattened proximal surface of the planta, except the joint of articulation itself, and it extends outward in a posterior direction a little beyond the remaining plantar edge. The surface of the auricle is covered over with many blunt, short spines and its lateral margin is bounded by a row of short rather pliable hairs, branched at their ends. When the planta is flexed the auricle is raised and its surface approaches the distal end of the tibia, its inner edge slipping up along the pecten spines and its outer hairy edge projecting into the opening which leads to the pollen basket. (See [fig. 8], b.) With each upward stroke of the auricle small masses of pollen which have been scraped from the plantar combs by the pecten are caught and compressed between the spiny surface of the auricle and the surface of the tibia above it. The pressure thus exerted forces the pasty pollen outward and upward, since it can not escape past the base of the pecten, and directs it into the entrance to the corbicula. The outward and upward slant of the auricular surface and the projecting hairs with which the outer edge of the auricle is supplied also aid in directing the pollen toward the basket. Sladen (1911) states that in this movement the weak wing of the auricle is forced backward, and thus allows the escape of pollen toward the basket entrance, but this appears both doubtful and unnecessary, since the angle of inclination of the auricular surface gives the pollen a natural outlet in the proper direction.

If the corbicula already contains a considerable amount of pollen the contributions which are added to it at each stroke of the auricle come in contact with that already deposited and form a part of this mass, which increases in amount by continued additions from below. If, however, the corbicula is empty and the process of loading is just beginning, the first small bits of pollen which enter the basket must be retained upon the floor of the chamber until a sufficient amount has accumulated to allow the long overcurving hairs to offer it effective support. The sticky consistency of the pollen renders it likely to retain contact with the basket, and certain structures near the entrance give additional support. Several small sharp spines, seven or eight in number, spring from the floor of the basket immediately within the entrance, and the entire lower edge of the corbicula is fringed with very small hairs which are branched at their ends. (See [fig. 3].) One large hair also springs from the floor of the basket, somewhat back from the entrance, which may aid in holding the pollen, but it can not function in this manner until a considerable amount has been collected.

Fig. 9.—Inner surface of the right hind leg of a worker bee which bears a complete load of pollen, a, Scratches in the pollen mass caused by the pressure of the long projecting hairs of the basket upon the pollen mass as it has been pushed up from below; b, groove in the pollen mass made by the strokes of the auricle as the mass projects outward and backward from the basket. (Original.)

As the pollen mass increases in size and hangs downward and backward over the pecten and auricle it shows upon its inner and lower surface a deep groove which runs outward from the entrance to the basket. (See [fig. 9], b.) This groove results from the continued impact of the outer end of the auricle upon the pollen mass. At each upward stroke of the auricle its outer point comes in contact with the stored pollen as soon as the mass begins to bulge backward from the basket.