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The Stelis, who is much smaller than the Chalicodoma, finds enough food in a single cell for the rearing of several of her grubs. The mother lays a number of eggs, which I have seen vary between the extremes of two and twelve, on the surface, next to the Mason's egg, which itself undergoes no outrage whatever. Things do not go so badly at first.
I do not know exactly how long the Stelis takes to make her entrance-shaft, as I have never had the opportunity or rather the patience to follow the work from start to finish; but what I do know is that a Chalicodoma of the Walls, incomparably larger and stronger than the parasite, when demolishing before my eyes the lid of a cell sealed only the day before, was unable to complete her undertaking in one afternoon.
That she should bore through the cocoons of the Stelis, a parasite of the mason bee, does not surprise me at all: I know how indifferent my bold visitor is to the nature of the victuals destined for her family. I have noticed her presence in the homes of bees differing greatly in size and habits: Anthophorae, Osmiae, Chalicodomae, Anthidia.
The lime of the road, mixed with saliva, yields a harder cement than red clay would do. At any rate, the Chalicodoma's nest is more or less white because of the source of its materials. When a red speck, a few millimetres wide, appears on this pale background, it is a sure sign that a Stelis has been that way.
The others, more expeditious feeders, have exhausted the victuals long before the victim has finished his normal repast. The swindled grub shrivels up and dies, while the gorged larvae of the Stelis begin to spin their strong little brown cocoons, pressed close together and lumped into one mass, so as to make the best use of the scanty space in the crowded dwelling.
The parasite has retained more than one feature of those industrious ancestors. So, for instance, the Psithyrus is extremely like the Bumble-bee, whose parasite and descendant she is. The Stelis preserves the ancestral characteristics of the Anthidium; the Coelioxys-bee recalls the Leaf-cutter.
I had to come to her assistance in order to discover, before the end of the day, the object of her housebreaking. When the Mason-bee's mortar has once set, its resistance is that of stone. Now the Stelis has not only to pierce the lid of the honey-store; she must also pierce the general casing of the nest. What a time it must take her to get through such a task, a gigantic one for her poor tools!
Atom by atom, she perforates the general enclosure and scoops out a shaft just sufficient for her passage; she reaches the lid of the cell and gnaws it until the coveted provisions appear in sight. It is a slow and painful process, in which the feeble Stelis wears herself out, for the mortar is much the same as Roman cement in hardness.
The first return and the last two seem to point to some relation between the abundance of provisions and the number of consumers. When the mother comes upon the bountiful larva of the masked Anthophora, she gives it half-a-hundred to feed; with the Stelis and the blue Osmia, niggardly rations both, she contents herself with half-a-dozen.
I picture the Stelis, before laying her own eggs, destroying the Chalicodoma's egg and eating it, as the Osmiae do among themselves; or I picture the dying thing, an irksome mass for the numerous spinners at work in a narrow habitation, being cut to pieces to make room for the medley of cocoons.
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