The walls are formed of fairly delicate materials, which must have been chosen in the coarse surrounding mass and kneaded with saliva.
The inside is carefully polished and upholstered with a thin waterproof film. We will cut short these details concerning the cells, which the Zebra Halictus has already shown us in greater perfection, leave the home to itself and come to the most striking feature in the life-history of the Halicti.
The Cylindrical Halictus is at work in the first days of May. It is a rule among the Hymenoptera for the males never to take part in the fatiguing work of nest-building. To construct cells and to amass victuals are occupations entirely foreign to their nature. This rule seems to have no exceptions; and the Halicti conform to it like the rest. It is therefore only to be expected that we should see no males shooting the underground rubbish outside the galleries. That is not their business.
But what does astonish us, when our attention is directed to it, is the total absence of any males in the vicinity of the burrows.
Although it is the rule that the males should be idle, it is also the rule for these idlers to keep near the galleries in course of construction, coming and going from door to door and hovering above the work-yards to seize the moment at which the unfecundated females will at last yield to their importunities.
Now here, despite the enormous population, despite my careful and incessant watch, it is impossible for me to distinguish a single male. And yet the distinction between the sexes is of the simplest.
It is not necessary to take hold of the male. He can be recognized even at a distance by his slenderer frame, by his long, narrow abdomen, by his red sash. They might easily suggest two different species. The female is a pale russet-brown; the male is black, with a few red segments to his abdomen. Well, during the May building-operations, there is not a Bee in sight clad in black, with a slender, red-belted abdomen; in short, not a male.
Though the males do not come to visit the environs of the burrows, they might be elsewhere, particularly on the flowers where the females go plundering. I did not fail to explore the fields, insect-net in hand. My search was invariably fruitless. On the other hand, those males, now nowhere to be found, are plentiful later, in September, along the borders of the paths, on the close-set flowers of the eringo.
This singular colony, reduced exclusively to mothers, made me suspect the existence of several generations a year, whereof one at least must possess the other sex. I continued therefore, when the building-who was over, to keep a daily watch on the establishment of the Cylindrical Halictus, in order to seize the favourable moment that would verify my suspicions. For six weeks, solitude reigned above the burrows: not a single Halictus appeared; and the path, trodden by the wayfarers, lost its little heaps of rubbish, the only signs of the excavations. There was nothing outside to show that the warmth down below was hatching populous swarms.
July comes and already a few little mounds of fresh earth betoken work going on underground in preparation for an exodus in the near future. As the males, among the Hymenoptera, are generally further advanced than the females and quit their natal cells earlier, it was important that I should witness the first exits made, so as to dispel the least shadow of a doubt. A violent exhumation would have a great advantage over the natural exit: it would place the population of the burrows immediately under my eyes, before the departure of either sex. In this way, nothing could escape from me and I was dispensed from a watch which, for all its attentiveness, was not to be relied upon absolutely. I therefore resolve upon a reconnaissance with the spade.
I dig down to the full depth of the galleries and remove large lumps of earth which I take in my hands and break very carefully so as to examine all the parts that may contain cells. Halicti in the perfect state predominate, most of them still lodged in their unbroken chambers. Though they are not quite so numerous, there are also plenty of pupae. I collect them of every shade of colour, from dead-white, the sign of a recent transformation, to smoky-brown, the mark of an approaching metamorphosis. Larvae, in small quantities, complete the harvest. They are in the state of torpor that precedes the appearance of the pupa.
I prepare boxes with a bed of fresh, sifted earth to receive the larvae and the pupae, which I lodge each in a sort of half-cell formed by the imprint of my finger. I will await the transformation to decide to which sex they belong. As for the perfect insects, they are inspected, counted and at once released.
In the very unlikely supposition that the distribution of the sexes might vary in different parts of the colony, I make a second excavation, at a few yards' distance from the other. It supplies me with another collection both of perfect insects and of pupae and larvae.
When the metamorphosis of the laggards is completed, which does not take many days, I proceed to take a general census. It gives me two hundred and fifty Halicti. Well, in this number of Bees, collected in the burrow before any have emerged, I perceive none, absolutely none but females; or, to be mathematically accurate, I find just one male, one alone; and he is so small and feeble that he dies without quite succeeding in divesting himself of his nymphal bands. This solitary male is certainly accidental. A female population of two hundred and forty-nine Halicti implies other males than this abortion, or rather implies none at all. I therefore eliminate him as an accident of no value and conclude that, in the Cylindrical Halictus, the July generation consists of females only.
