From what I have read:
If you are using a wood block for Orchard Mason Bees, the holes should be
5/16" in diameter, 3/4" on center from each other, and 6" deep. The depth is
important since only at this depth will you be providing enough room for a
proper male/female ratio. A fertile female (there are no "queens" with these
solitary bees) will lay females first in the depth of the hole followed by
males. If the hole is less than 6" in depth she lays a higher proportion of
males than females or no females at all. Therefore, upon emergence the
following February/March, there may not be enough of both sexes to mate and
repeat the cycle. I have also read that you can clean out the previous years
holes with your drill bit but replacing an old block with a new one yearly
is prefered. Molds, mites and other undesirables can take a footing in old
habitat.

----- Original Message -----
From: "john f. mesinger" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 07, 2001 6:24 AM
Subject: Re: Mason Bees


>         I got  a 6in block of 4X4in wood with a square pattern of many
> holes drilled 2+in deep and a chicken wire anti bird screen over the face
> several inches out fromm a class project in a rural HS in SW VA  two years
> ago; put it on  a 4 ft post, it was filled and plugged with mud by Mason
> beed queen or queens. They hatched. I cleaned the holes last winter and
> there were no repeats last year.
>
> John F. Mesinger
> [log in to unmask]