Melody Kendall

As a child, a bee sighting was usually accompanied by a lot of screaming and general chaos. As I matured bees were given a wide berth and usually avoided.  When raising our family we removed any and all plants that attract bees,  something that I have come to regret as a more educated and seasoned UC Master Gardener. 

About twenty years ago we noticed large black bees congregating around our wooden pergola. Closer inspection showed  bees entering and exiting holes that had been neatly drilled into the support beams.  My husband was not amused.  Having been recently enlightened about bees and pollinators in general I suggested a cautious approach instead of wholesale slaughter of them. We took one of the bees that had died of natural causes to the Napa County Agricultural Commissioner's office and asked them about the cause and future progress of this infestation. The Ag Commissioner's office staff provided us with information and suggestions. Basically, the bees are benign but would continue to ‘drill' holes. It was suggested that we fill the holes and paint the support beams. 

There are three species of Carpenter bees here in California: Xylocopa varipuncta , X. californica & X. tabaniformis orpifex.  I'm not sure which one that we have.  All three species are the largest bees in California at around an inch long. The Carpenter Bee eggs are the largest of all insect eggs at about ½ inch long. The females are black and shiny and the males are large and colored gold or yellow. The females are the ‘carpenters' using their mandibles to drill deep holes eight to ten inches in depth in untreated wood. They will sting but only when provoked. The males don't sting, are territorial and spend their time lying in wait for passing females. 

Carpenter Bees are great pollinators in our area and their specialty is California native plants. Seeing one flying around pollinating the garden is quite exhilarating, due in no small part to their massive size and loud buzzing. Because they have great potential for pollinating crops there is ongoing research as to their value in greenhouse ‘buzz-pollination'.  This is where the bee hovers at the opening of the flower and using its beating wings creates movement via sonic waves that causes the pollen in the flower to release and thus fertilize the plant.  The size of this bee makes entering some flowers a problem so they use ‘buzz-pollination' and ‘stealing the nectar' methods to get the nectar from many flowers.  When ‘stealing the nectar' the bee actually cuts the corolla of the flowers that have narrow openings and steals the nectar without pollinating the flower.  

Since we noticed their living arrangements we have done nothing to curtail the carpenter bees in our yard and, in those twenty years they have not excavated any additional holes in our pergola. The bees continue to buzz quite loudly during the summer, pollinating the garden and bringing home food to their nests.  In the winter months they quietly sleep in their snug tunnels. The only downside to their chosen habitat is the bee ‘frass' left on the deck furniture.  In my opinion it's a perfect cohabitational living arrangement considering all of the Carpenter Bee's wonderful beneficial attributes. 

Information links:

UC IPM         http://ipm.ucanr.edu/PMG/PESTNOTES/pn7417.html

UC News about Entomology and Nematology

https://ucanr.edu/blogs/entomology/index.cfm?tagname=carpenter%20bees

Napa Master Gardeners are available to answer garden questions by email: mastergardeners@countyofnapa.org. or phone at 707-253-4143.  Volunteers will get back to you after they research answers to your questions.

Visit our website: napamg.ucanr.edu to find answers to all of your horticultural questions.

Photo credits: Mel Kendall