> "Our" bees are smaller than in the past in the southwestern
> U.S. The desert-adapted feral bees I collected from 1987-1993
> were not necessarily small; in  fact, some were quite large
> ( around 9.22 mm forewing length). We have virtually no large
> bees here now.  It would seem reasonable to expect different
> results with pollen traps.

I have been wondering about excluders for some time now, and measured a variety
of them I have accumulated, ones that were manufactured at various times over
the past 60 years or so.  The results are on my web site referenced in my last
post on this topic several months back (Item #29613 (24 Oct 1999 21:41) -
Excluder Variability).

It seems to me, from my measurements, that someone just made an excluder that
worked for him back 50 years ago or more, and everyone else just copied it
because they are all pretty much the same in the width of the slits, although
the direction and thickness of the wires vary.

For some bees, getting through is a breeze, for others it must be a crunch.  One
of the bee scientists I was visiting with the other day in San Diego mentioned
that queens had been seen with dents in the thorax, and the assumption was that
it was from her forcing her way through an excluder.  Others agreed.

I personally have used 5 mesh hardware cloth as an excluder with good success.
I think each hole in such screen is quite a bit wider than the .062 gaps that
were typical in the excluders I measured.

Taking an inch (1.000") and dividing it into 5 gives 5 x 0.200", including the
wire on one  side of the square.   Since 0.200-0.062 = 0.138" and the wire is
between 0.020 and 0.30 depending on the maker --  we have a hole that is
0.138-0.025(the average wire size)=0.113" square in five mesh hardware cloth
unless I measured or reckoned wrong.

When we compare that to the 0.062 spacing in excluders, we see it is almost
double, but it works.  Is it because of the shape (square) of the hole compared
to the slit in an excluder?

Does anyone have a zinc excluder on hand to measure?  Since a zinc excluder is
very thin, I should think the slit in it should be a little different than the
one in a wire excluder which has more thickness.

Anyhow, I wandered around here to check my numbers before posting, but we can't
find the dial callipers and, besides, the excluders are all 1/4 mile away in a
shed out in the cold.

Maybe some will check my numbers and confirm my observations?

allen