Had I tried to avoid these useless apparatus by choosing tubes of larger calibre, I should have encountered another drawback: the medium-sized mothers, finding themselves almost comfortable, would have decided to lodge females there.

I had to be prepared for it: as each mother selected her house at will and as I was unable to interfere in her choice, a narrow tube would be colonized or not, according as the Osmia who owned it was or was not able to make her way inside.
There remain some forty pairs of tubes with both galleries colonized.
In these there are two things to take into consideration.

The narrow rear tubes of 5 or 5 1/2 millimetres (.195 to .214 inch .-- Translator's Note.)--and these are the most numerous--contain males and males only, but in short series, between one and five.

The mother is here so much hampered in her work that they are rarely occupied from end to end; the Osmia seems in a hurry to leave them and to go and colonize the front tube, whose ample space will leave her the liberty of movement necessary for her operations.

The other rear tubes, the minority, whose diameter is about 6 millimetres (.234 inch .-- Translator's Note.), contain sometimes only females and sometimes females at the back and males towards the opening.