By John V. Richardson Jr.


“What type of native bees are most likely to use bee houses?  How many eggs are typically laid in a single hole and how does the depth of the hole influence the ratio of male/female offspring?  (And, how do they get out?)”



In the United States, interest in bee houses can be traced to at least the mid-19th century, when US Patent number 1612 was issued in 1840 to Robert Martin of Ohio.[i]  Without assistance, native or solitary North American bees inhabit holes in wood, stems of plants, or tunnels in the ground.  So, only some bees (such as carpenter bees, leafcutter bees, and Mason bees, to name a few) will inhabit untreated, wooden posts.


According to the NSAIS‘s website called Alternative Pollinators: Native Bees: “Eggs [of Mason bees] are laid in tubular cells, with up to 11 cells per nest. The female determines the sex of the egg and lays male eggs closer to the entrance hole.  This assists in perpetuating the species in two ways.  First, the males are more accessible to predators than females, and second, males emerge several days before females.  If the female ‘at the back of the line’ emerges first, she opens the cell of the next female and nips at her to urge her out of the nest.  This continues down the line until all females have emerged from a single nest tube.”[ii]


The Xerces Society asserts that size matters: “solitary bees…can be very particular about hole diameters.”[iii]  Whenever hole size is mentioned in the professional literature, so is the Orchard Mason Bee (Osmia spp.), of which there are 140 species.


In fact, there are several assertions in the literature related to mason bees.  The first is a thesis and a directional hypothesis: “The most effective hole size is close to 5/16" in diameter and 6" deep.  If holes of less depth are used, the nesting females will produce fewer female and more male progeny; if deeper holes are used, the extra space is wasted,” according to Dr. Philip Torchio, a retired entomologist from the USDA Bee Lab in Logan.[iv]  


Another, but alternate, hypothesis states:  “[The female OMB] chooses holes slightly larger than her body, usually 1/4 to 3/8 inches in diameter…Trap nests can be made by drilling holes 1/4 to 3/8 inches in diameter and 3 to 6 inches deep,” according to Washington State University’s “Gardening in Washington: Library: Orchard Mason Bee” website.[v]  Finally, a recent US Patent claims that the carpenter bees (Xylocopa spp.) can be trapped in holes of “a diameter within the range of from about 5/16 inch to 1/2 inch,” according to US Patent 6766611 (2004).[vi]


Today, we recognize more than 3,500 native or solitary North American bee species (of which 500 are sweat bees and another 500 are digger bees).  So, can one generalize to all 3,500 bees based on these assertions about just a couple of species?  More work needs to be undertaken before one can do so confidently.





[i] “Beehive” (1840) at (accessed 4 November 2008).


[ii] which cites Christopher  O'Toole and Anthony Raw, Bees of the World (New York: Facts on File, 1991) as its source (accessed 4 November 2008).


[iii] (accessed 3 November 2008).


[iv] Personal Communication from Torchio, Philip F. See also, “Use of Osmia lignaria propinqua (Hymenoptera: Megachilidae) as a Mobile Pollinator of Orchard Crops,” Environmental Entomology 20 (Number 2, April 1991): 590-596 and P. F. Torchio, "Factors affecting cocoon orientation in Osmia lignaria propinqua Cresson", Journal of the Kansas Entomological Society 53 (1980): 386-400;  P. F. Torchio & V. J. Tepedino, "Sex ratio, body size and seasonality in a solitary bee, Osmia lignaria propinqua Cresson", Evolution 34 (1980):: 993-1003;  and P. F. Torchio, "Use of non-honey bee species as pollinators of crops", Proceedings of the Entomological Society of Ontario 118 (1987): 111-124.


[v] (accessed 3 November 2008).


[vi] Carpenter Bee Trap (2004) at (accessed 4 November 2008).