MALES AND FEMALES
These differ from each other very greatly in many cases. Eccentricity in structure almost always occurs in the male; excess of coloration usually in the female. In size the male is generally the smaller and the less robustly built of the two. Among the pollen-collectors, the male is usually less densely clothed with hairs than the ♀. In the fossors this rule is rather reversed, but in that section neither sex is densely clothed with hairs as are most of the pollenigerous bees.
The male has normally thirteen joints in its antennæ, and the female only twelve. There are exceptions to this rule amongst the ants and in certain fossors of the genus Crabro, some species of which have the antennæ considerably distorted, and have two joints welded apparently into one. Another distinction between the sexes is that the male has seven dorsal segments
of the body exposed to view, and the female only six. In the males of some of those bees which collect pollen on the underside of the body, the body above terminates with the sixth segment. This is because the seventh is turned over on to the underside, and faces downwards, its apex pointing towards the head. This arrangement of course leaves less room for the regular ventral segments, and the usual apical segments are in consequence "telescoped" up under the fourth, so that the apical opening of the body lies on its underside between the fourth ventral and the inverted seventh dorsal segments. This very curious structure occurs only in those bees whose females collect pollen on the underside, and the reason of it is to me quite inexplicable. The females of a few of the fossors are destitute of wings; but in this country we have no wingless males, except in the case of one little ant (Formicoxenus); this lives in the nest of the common large red ant, and its male can hardly be known from the worker except by the number of joints in the antennæ and the absence of a sting. In the cases where the female is wingless, the male as a rule is much the larger of the two sexes.
There are few more puzzling questions than those which arise over these eccentricities of structure; they seem to have no relation to any habits of the creatures' lives so far as we can judge, neither can one suggest any useful purpose which they can serve. In some groups the males of all the species seem built on one regular plan—in others the males of each species seem to vie with the next as to what eccentricity of structure in antennæ or legs or apex of the body it can exhibit. In numbers, the males probably considerably exceed the females, and are far more frequently met with, as they seem to be less particular as to weather, and not being intent on obtaining food for their offspring they fly about more casually, and certainly are more in evidence generally.
The great difference in structure, etc., between the males and females makes the work of pairing the sexes very difficult, especially in those genera where the males and females appear together only for a few weeks, as is the case in Halictus and Sphecodes. If one visits a locality in the spring one may catch any number of females of Halictus, but no males appear till the late
summer or autumn, and, unless one visits the same spot again when both sexes are out, it is impossible to associate males and females. I have at the present moment in my collection several males, which, being in doubt about myself, I have communicated to continental authorities, who have returned them to me as possibly the male of so and so! and we shall have to remain in uncertainty about them till some one happens to take both sexes together, when the mystery will be solved.
In time of appearance the males always precede the females—in burrows, such as those of the leaf-cutting bees, etc., it may seem puzzling as to how this is arranged, as one cell is placed over the other so that those lower down in the tube cannot pass those higher up. This difficulty is got over by the arrangement that the first eggs laid by the mother bee are female and the last male, so that those at the top belong to this latter sex; these emerge as soon as the warmth of the sun is great enough to energize them sufficiently to break through their cell covering, when they emerge and wait for the appearance of their females. The males of
some species of Andrena seem to take great pleasure in flying rapidly up and down hedgerows, hardly ever settling, and apparently far away from their females, which are probably pollen collecting in dandelions or some such flowers in the neighbourhood.