Ten Rules for Mason Bees

After 20 years, many thousand bees, many successes, and several failures, here are:

The Mason Bee Rules
Glen Buschmann

Rule #  1:   Mason bees need fresh housing each year. 

Rule #  2:   Mason bees need the right type of housing.

Rule #  3:   Mason bees choose nests based on nearby food.

Rule #  4:   Mason bees need mud nearby, to make nest cells. 

Rule #  5:   Mason bees work in cool - but not cold  - weather.

Rule #  6:   Mason bees pollinate from March through May.

Rule #  7:   Mason bees are fragile from June into September

Rule #  8:   Mason bees ought to be sheltered during the winter. 

Rule #  9:   Mason bees are a solitary bee.

Rule #10:   Mason bees can become too plentiful. 


RULE # 1:  Mason bees need fresh housing each year. 
    There is no way around this rule, and its violation is the source of more trouble than any other rule.  Your success with Mason bees comes with your grasp of this rule and your willingness to follow it.  Find a system of housing which works for you and which you can abide by each year.  Experiment.  BUT, if you ignore the rule of fresh (clean / new) housing, your bee success will plummet and in a few years you WILL NOT HAVE  a viable bee population.

Rule # 2:  Mason bees need the right type of housing.
    This is actually a pretty easy rule.  Mason bees require a physical structure for their larval cells - but they are dedicated versatile builders.  Nests can be cardboard tubes, holes in wooden blocks, lengths of plant reeds, home-rolled tubes, etc.  They’ll nest under siding, in empty snail shells, in a cliff-face. 
    Be sure the nest material is non-toxic.  Treated lumber will poison the larval food.  Plastic is “safe”, but doesn’t breath; bees also have a harder time making mud stick to plastic walls.
    A nest tunnel of 5/16” inside–diameter is often suggested.  But tunnels 3/8” diameter also work well: the bee needs more mud for each cell, but fits each tunnel with more cells and thus bees.

Rule # 3:  Mason bees choose nests based on nearby food.
    If mason bees emerge from their winter slumber and find plenty of pollen and nectar within a couple hundred feet, they’ll stay put.  But if better food is down the road they may shift operations.  If nothing is blooming, you might loose your bees.

Rule # 4:  Mason bees need mud, nearby, to make nest cells. 
    Mason bees need a nearby source of mud (moist dirt).  Some people make a mud-pit.  If your soil is very sandy, add some soil with a higher clay content.  The more convenient the mud, the easier / faster it is for the bee to build, as one cell can take 25 or more mud trips, (preceded by this many pollen trips), before the cell is completed.

Rule # 5:  Mason bees work in cool - but not cold  - weather.
    It is common for Mason bees to wait until 11:00 a.m. or noon before getting to work.  The warmer they are, the sooner they get up.  They can work in overcast, even drizzle, but not in rain and wind.  In general they are active when it becomes 55° and warmer.  If their housing faces southeast and warms up with morning sun, and is sheltered from the wind, they may start earlier.  It is common for them to work until dusk.  At night they usually tuck themselves into an open hole head first with their hind end almost sticking out.

Rule # 6:  Mason bees pollinate from March through May.
    Mason bees are active adults only in the early spring.  They are excellent pollinators of fruit trees and early flowering plants but by early June their adult reproductive phase has ended.  Plants which need pollinating after mid or late May need help from other sources.

Rule # 7:  Mason bees are fragile from June into September.
    If you relocate Mason bees during the summer - their pupation time - move them gently with minimal jostling.  By late September, they are adults and quite rugged.  But as pupae, they can die with rough handling.
    Late Spring into Summer is also a time when some pests may be at their peak.  Two tried and tested strategies are sheltering Mason bees from parasites by placing filled nest boxes behind super-fine mesh that resists parasitic insects, and moving the nests to where the filled tunnels face a wall, which also reduces easy access by larger predating animals.

Rule # 8:  Mason bees ought to be sheltered during the winter. 
    If you have not already done so, by the end of October put Mason bees into storage; by early March return the bees outside.  Fall is also the time to open some nest chambers and inspect the cocoons; with tray type housing you free the cocoons, clean them, and store them loose.
    Unheated sheds and garages are suitable for overwintering.  Storage in refrigerators works IF the humidity does not drop too low - a problem with frost-free refrigerators (too low a humidity can kill).  Add some humidity to get around the problem, but don’t let mold and carbon dioxide build up.   
    Mason bees take considerable cold, but prolonged sub-freezing weather can kill hibernating bees.  Although the cocoons are weather resistant, the housing is not.  Paper nest tubes spoil when wet; plastic nests don’t breathe; wood blocks can split.   Every cocoon is coated with frass (fecal pellets) left by the larval bee.  When frass gets wet it grows moldy: this is unhealthy.

Rule # 9:  Mason bees are a solitary bee.
    This is a solitary bee.  Each female is tolerant of her neighbor, but not cooperating with her.  While at the peak of activity the population may resemble a hive, it is not.  It is an apartment and you are the landlord.  Mason bees do not tend their progeny.  They have no traffic cop at a hive entrance.  They are not daughters of one queen.  They work alone.

Rule #10:   Mason bees can become too plentiful.
    Mason bees are easy to raise - a good “starter” bee.  When providing everything right, you can increase six-fold a small number of bees within a year.  Don’t get overeager and raise more bees than an area will support or you can manage!  Exceed the limit and stresses increase, mix-ups increase, pests increase.  Too many bees at one time can strip the pollen resources, or just as likely result in more fruit on a tree than it can handle.
    We can't fully say how many is too many.  Mason bees are VERY efficient fruit tree pollinators.  Research in orchards suggests that as few as two or three female mason bees can effectively pollinate an apple tree and 250 to 300 females can pollinate one acre of apples. It may be that the cooler, wetter weather west of the Cascades is less pollinator efficient; even mason bees, while fairly tolerant of poor weather, will not work when it is really cold or rainy.  It is also clear that a diverse home garden easily supports more than this small number. 
    Up to a point competition and activity may stimulate interest from other bees - think of people following a "grand opening".  But a bee must choose her nest site quickly.  A native bee with similar nesting requirements and emerging later - in the middle of too much intense activity of the "artificial" bee - may move on in search of less frenzied nesting sites.  This would result in a garden with a SMALLER population of late season bees.
    Be observant.  There are thousands of different native bees.  Learn about other bees by reading AND investigating - and try to “raise” some other bees.  Bumblebees use abandoned mice nests; leafcutter bees line tunnels with pieces of leaves, sweat bees dig “mines” underground.  Choose new plants by watching bees in a a park or at a nursery.  Create new and different nesting opportunities which encourage diversity.  Record what you see. 

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Birds, Bees, & Butterflies
Glen Buschmann  •  Janet Partlow
olypollinators@aol.com  •  olypollinators.blogspot.com
PO Box 11464  •  Olympia, WA,   98508  •  360-352-9009