I would think that the straws you put out are simply more attractive to them. They'll go to the habitat that best suits them.
Here's the thing with drilled holes... even with a nice sharp, good quality brad-point drill bit, the wood fibers are going to wrap sideways and hug the hole walls as you drill. So you will end up with many wood fibers still attached but pushed up against the hole walls. As time passes, especially when exposed to outdoor conditions, those wood fibers tend to pop back up. Not so noticeable to you or me, but a major hazard to a mason bee. And this is if you use a proper wood-specific drill bit designed to drill clean holes. A less appropriate drill bit will give even worse results. I used to spend alot of time trying to get this right and decided there were simply better ways to house mason bees. Wood fibers like this will tear up the mason bees wings, or so I've been told by Dave Hunter of Crown Bees. Here's a link that you might find useful:
[url:2h7b2ecw]http://www.crownbees.com/blog/post/mason-bee-tubes-and-straws-which-are-best[/url:2h7b2ecw]

You may want to try Foerstner drill bits as an alternative to spade bits, twist bits or brad point bits.

Like any woodworking tool sharpness is critical. Just because a tool is new does not mean it is sharp.

The only problem with Foerstner bits (besides their higher cost) is that they may not be longer enough to bore a hole to a five inch depth.

If you could wrap a piece of sandpaper around an appropriate sized dowel or metal rod, you could sand the inside hole walls (inserting the dowel or rod into the drill chuck).

Additionally some older wood finishers will apply glue sizing to wood surfaces preparatory to final sanding. If you dilute white glue with water (say 1 part glue to 10 parts water) and apply this "sizing", two things occur: the wood fibers swell (and straighten) from the adsorbed water, and the adhesive sets/hardens them in this position. When the wood is subsequently sanded, you get a much cleaner and smoother surface.

White glue is polyvinyl acetate and is pretty safe environmentally. If you are especially concerned, use the school type liquid white glue (which I assume kids still eat) and dilute it more (1:15 or 1:20).

If the sandpaper becomes rapidly clogged with glue, it indicates that the adhesive needs to be further diluted, or that you have not allowed the wood to fully dry.

Shellac could also be used. Shellac is diluted with alcohol instead of water but both water and denatured alcohol (e. g. methanol or ethanol) are polar solvents which will be adsorbed by wood cellulose and hemicelloloses. and thus swell the fibers. When the alcohol evaporates, the shellac will harden and thus "size" the wood.

Originally shellac was made from an exudate from bugs; I don't know if that is still true.

captainbilly -- I would not worry one iota about sealing the wood to the point that the moisture in pollen would cause mold. Wood is porous and a single coating of any dilute sealer (sizing) that is subsequently sanded would create such a minimal barrier to the vaporous transmission of water vapor as to be almost negligible. If you are cross boring a hole, you are exposing large areas of end grain which transmit water (water vapor) at about 100 times the rate of cross grain (between cells) transmission.

Further, according to a USDA Forest Products Lab Research Paper (FPL 462) entitled: "The Moisture Excluding Effectiveness of Finishes on Wood Surfaces" indicates that a single coating of orange shellac (undiluted) has a MME (Moisture Excluding Effectiveness) for 1 day of 59%, for seven days of 9% and 14 days of 2%. No data is available for white glue because all Latex-like coating were pigmented. (but showed values similar to shellac). With diluted shellac subsequently sanded, the probable MME in those holes would be at most 1/10th of the above values. Hell, the mud used to seal the hole is probably much wetter and that doesn't seem to cause pollen molding.

I don't know what the average moisture content of pollen is but the Equilibrium Moisture Content (EMC) of outdoor wood in summer is somewhere around 12 to 16%. I would expect pollen values to be somewhat similar, but if not the mass of polllen proportional to the mass of wood surrounding the pollen would be almost insignificant. The pollen would quickly equilbrate to the wood's EMC. Generally EMC's of less than 20% preclude the growth of bacteria, molds and fungi in wood itself (surface wetting is another issue entirely).

Try a sharp Foerstner bit as a first step.

And if you do try the trick of wrapping sandpaper around a dowel or metal rod chucked in a drill to sand the hole, if you reverse the rotation from that of the drilling process, any bent over fibers (not cleanly cut from drilling) would likely be sanded off by this means.

LeeN
Wood Technologist
M. S. Penn St '79

For some really good information on native pollinators see: [url:u0z9adpx]http://www.attra.org/attra-pub/nativebee.html[/url:u0z9adpx]

Remember that hole depth is critical for the sex of the offspring (3.5 inch deep holes produce mostly males; 5.5 inch deep holes produce more females.

I scrounged some 4" x 12" cutoffs (18" long) from a construction site and bored 5/16" x 5.5" deep holes from opposite sides of the block. Lots and lots of holes; and mounted one block on my shop wall underneath the eaves; and another to a post for an open air shed. I really need to check 'em but I also believe that the bees will use 'em as they choose.

Because there are other native pollinators, I need to create some other blocks with smaller sized holes for these species. (in my spare time, Yah)

And by trade I consider myself a joiner (primarily building furniture from solid hardwoods) rather than a carpenter, so I rarely nail things down -- I cut joints (use to roll some too) and glue them together.

LeeN

Three brief thoughts:

As long as the hole size is appropriate -- go for it. You can check hole diameter by using the solid (non-fluted) end of a drill bit. If slightly undersized, you can enlarge the hole but be sure that the bamboo is held securely (definitely don't try holding it with your hands while operating a power drill).

If the bamboo has not been properly seasoned before it was stored, it may be innoculated with all sorts of yeastie/beasties (molds, bacteria and fungi). Five minutes at 150 degree F in an oven will effectively sterilize 'em.

I would seal the ends with something other than wax. There is a product called water putty (likely available at hardware or paint stores) that would be my preference/recommendation. Before wood filler came in premixed containers, this was what was available for filling holes. It is a powder that you mix with water that sets with about 10 minutes (so only mix about 1/3 of a cup of powder at a time). Take a dab of the wet mixture (not too wet now -- think the consistency of cream cheese) on your finger and squish it into the hole and with your same finger, wipe away any excess on the sides; and then do another, etc. If you're not overly messy, there will no need to sand or chip off any excess.