This article discusses the proper way to identify and then remove an unwanted honey bee colony inside a building wall or other cavity.
Page top photo: a Mexican honey bee collecting pollen from a false jasmine plant, photographed by the author in San Miguel de Allende, Guanajuato, Mexico, in January 2024.
The author is a building environmental inspector and forensic microscopist, and a previous member of NPMA, National Pest Management Association. He has inspected, constructed, restored and repaired, buildings and diagnosed and repaired building and building-related environmental problems, including insect damage, since the 1970s.
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Bottom line: Watch out: it's best to avoid killing bees if you find them swarming in or around your home. But if bees are moving into your building there area two different situations:
Given recent decimations of bee populations world wide we desperately need all the bees we can get. If you don't think there is a serious bee shortage, just take a look at people in China climbing trees with Q-tips to pollinate flowers on fruit trees.
Further, as we mentioned above, leaving a large clump of dead bees and honeycombs in a building wall can lead to a new series of complaints.
Photo above: months after a honeybee colony in this building had been killed by using a pesticide, the wall began to smell horrible. Ultimately the owners had to have the wall opened - in this case from the exterior side.
The dead bees along with a mess of honeycomb could then be removed. Had the owners known what to do sooner, the bees could have been removed without killing them and the extent of demolition and cleaning could have been less.
Details: Here, using reader Q&As to provide examples, we give advice for safe and effective removal of an invasion of honey bees who have taken up residence, perhaps even built honeycombs in a building cavity - most-often building walls.
I found this odd stain pattern and black speckled material in my home. This is between the joists in my basement. I removed Sheetrock and insulation and found it. Thanks - M.R. 1010/17/2013 - updated 08/2024 - Ed.
I've been thinking about this and your photo - it's not something I've seen inside a building before; the growth pattern looks a bit like algae fronds, but on closer inspection I think those black dots may be fungal spores or ... something else (remains from an insect colony).
Mold growing in the pattern of a fern leaf or bracken pattern is not one I've found before.
On the side of what looks like a floor joist in your photo is what looks a bit like fungal growth of basidiomycetes - I don't know from such limited data; IF it's fungus there you should be looking for rot and structural damage;
Is that shiny property in the photo because the surfaces are wet? Where is this - geography, building type?
If you can collect suspect material on a tape sample (or if not try a razor blade and a clean plastic baggie or hard plastic container) you are welcome to send me a couple of samples and I'll take a look in the lab. For tape samples try the procedure (and address)
Reader Michael Sears said: these may be marks from honeybee or feral bee honeycombs
I just saw your image inspectapedia.com/mold/Algae_or_Mold_939_MR_DJFs.jpg [the photograph just above]
I believe these are marks left over from the removal of a bee hive. The fern pattern is where the honey comb connected to the subfloor. - 4/7/2014,
Thanks Michael. I took a look at several resources on how people remove honey bee colonies from buildings (traps are good but there are also special vacuums that don't harm the bees), before finding one of them, the E.C. Mussen (U.C. Davis) citation below that included photos not of the marks left behind by a honeybee comb on a building surface but of some feral beehive structures that could have made marks similar to those in the photo above.
Additional information is in a nice article by Keith Delaplane at the University of Georgia, also cited below.
In Delaplane's photos we see that some of the bee honeycombs built in a building wall cavity (and presumably similarly under a floor as in our photo above) are placed on-edge in a manner (see Delaplane, Fig. 3) --that might leave the marks we are discussing.
Photo: another useful pollinator, though not a honeybee, may be mistaken for one though it's in fact much larger and fatter. Our photo above shows a Tricoloured Bumble Bee or Orange-belted bumblebee (Bobmus ternarius) photographed in Two Harbors Minnesota in May, 2024.
Thanks for the reply. I don't see any structural damage to the floor joist or sub-floor. Whatever it is, appears to be on the surface.
I'm located outside of Hudson, NY. My house was built in the 70's and we have lived here for 4 years. When I moved in the basement was finished, Hurricane Irene changed that. We got flooded, a significant portion of the foundation cracked and began to collapse. We had mold everywhere. Long story short, we scrapped everything in the basement, gutted it, rebuilt the foundation and started over.
This spot of fungus or mold, however, was not touched by the flood. Which is why I hadn't removed the drywall and insulation until now. And I was surprised to find it, because everything around it is in good shape.
The shine in the picture is probably from bleach solution I sprayed on it. However the fungus had a sheen before I sprayed it. It has a waxy appearance, but it's not soft, in fact I had a hard time trying to scrape it with a putty knife. The bleach solution and scraping have not had much affect.
I would like to test this to see what it is. How much do these tests usually cost? My primary concern is the health of my family, and second I want to remove any problems before I finish my basement.
Sharp photos would be helpful, not just closeups, but the situation in the basement and perhaps an outside photo of the house distant enough that I can see what surface drainage looks like. I'll look at your samples pro-bono - in our own forensic laboratory.
If you can't get something on a tape, best possible sample would be a wood scrap (not a wood "scraping" that had the material on its surface; second best is to try to carefully cut or slice off a sample and package it in a rigid container so it's not turned into powder before I can see its structural properties.
Knowing the history of the house, prior flooding, is helpful in evaluating the risk of hidden mold. About the prior flood and cleanup, you want to be sure that moisture from flooded lower floors didn't create a hidden hazard in upper building wall cavities or ceiling cavities.
The sample received was wood fragments ranging from about 1/2cm to ultra-fine powder. I prepared test samples by trying a tape lift from the largest fragments (best results) and additional samples from pulverized fragments and from dust in the plastic bag containing the original fragments.
Details of the actual slide preparation from the scraping sample submitted by M.R. are found
at MICROSCOPE SLIDE BULK SAMPLE PREP.
These samples were mounted in lacto-phenol with a trace of cotton-blue dye and were examined microscopically at various magnifications up to 1200x.
Given that I though we were looking at a fern-like bracken mold growth pattern I suspected there may have been an artifact such as a residue left by prior plant material pressed on the subfloor. It seems I was wrong.
And I was surprised to find plenty of fungal spores in the scrapings you sent me, though unfortunately sending scrapings rather than a tape lift of the surface fails to capture the growth patterns themselves - data that would have been most helpful.
Spores varied in size, shape and color, probably due to variations in bleach treatment and hydration in my mountant; the most well defined photos (below) resemble Periconia-like fungal spores, but of a too-light color - a condition that I guess could be due to having applied bleach.
My identification is uncertain due to sample condition, but I've asked a couple of fellow microscopists for help in case anyone has seen this fern-like or bracken-like fungal growth pattern before.
I could not locate the pattern in my references and will continue to research the matter.
We welcome comments (CONTACT) from others about the identification of this fungus.
Bleaching mold, as you report you did, is pretty irrelevant.
See BLEACHING MOLD, Advice about
As we can see even in this sample, it does not "kill" every spore - some remain viable - or at least the spore colors and physical condition vary widely from fragments and hyaline spores to dark brown or bleached yellow fungal spores.
More to the point, depending on the species, some fungal spores remain allergenic or toxic even if non-viable (bleached to death) and may still contain mycotoxins. Such mold at high levels and particularly if airborne could still be a problem for some people in the building.
The proper approach to indoor mold contamination is to remove the mold, clean the surfaces, and fix the original cause for mold growth.
Given the conditions you've described I'd not be particularly worried about the remaining spores - once you've cleaned off what can be physically removed, dried, and then sealed the surface your attention needs to be on finding and fixing sources of leaks, water entry, high moisture.
I attach one of my fungal spore photos for comparison. If you are able to obtain a clear adhesive tape lift of the surface in the actual growth pattern we saw in your original photograph that would be most helpful.
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Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
Question: what to do about active bees nest in building siding
Hello! We have a client who purchased a home that seems to have an active bees nest in the siding:
Bees have been observed coming in and out of the gap(s) between the siding.
How can we manage these bees and repair the exterior? Thanks for reading and any guidance!
Reply:
@christina,
OK so to manage or get rid of these bees in building siding and to make the appropriate repair we need to
1. First step: Identify what kind of bees are invading or have nested in the building's siding
Watch out: If these are honey bees we'll need to proceed to remove the hive with some thought because, despite a bit or news of some bee recovery, in many parts of the world including the U.S. so much of the bee population has died off that the critical task of pollinating crops (so that we humans have food) has led to a whole industry of people who drive across the country with tractor trailers of bees that they rent out to farmers each year when it's time to pollinate their crops.Photo above: an American honeybee collecting pollen. (University of California Agriculture & Natural Resources, Statewide Integrated Pest Management Program - E.C. Muyssen 2012)
A honeybee colony in a building wall will need to be removed by a beekeeper
If the bees in question are Honeybees, (smaller bees, orange and black stripes - photo above excerpted from Muyssen-2012) see
HONEY BEES in BUILDING WALLS inspectapedia.com/structure/Honey-bees-in-walls.php
where we include links to expert advice both at some agricultural websites and as PDFs that you can down load, print, and give to your client.To have a honeybee colony established in the building removed your client should call a local beekeeper.
Watch out: while it may be legal (depending on where your client's building is located) to use a pesticide to kill the honeybee colony in the building walls, in own experience going back nearly 50 years, doing that can create a stinky mess in the building walls.
Killing the bees in the wall can leave honeycombs (some of our clients later had problems with other insects or animals attracted to the honey). and as happened with one of our clients back in 1990, the large dead bee colony in the wall began to rot and stink (photo below).
Photo above: ultimately the wall had to be opened and the cavity cleaned of dead bees and dusty honeycombs.
What if they're not honeybees?
If these are carpenter bees (photo below) the problem is usually much more limited, and though it'd be better not to kill any bees, I'm more sanguine about treating a carpenter bee infestation.
So take a look at CARPENTER BEES inspectapedia.com/structure/Carpenter_Bees.php for help identifying these insects - easily spotted as big fat black and yellow bees that usually invade the edges of wooden boards and trim. (Photos above and below)
2. About repairing damage, from bees, first I need to know just what sort of damage needs attention. Before having some idea what that is, any advice I could give would be just too speculative to be useful.
Honeybees do not damage building structures, though on occasion they may damage interior drywall - look for a damp spot on an interior wall that seems to be increasing in size or honeybees actually entering the building through a hole they've made in the drywall. (Muyssen-2012)
It would also be helpful to see some photos - of the bees, of the damage - one photo per comment, as many comments as you like.
It would also be helpful to know the age, type of building, and its location where the bees are taking up residence.
Please post and continue this discussion at inspectapedia.com/structure/Honey-bees-in-walls.php where we'll also repeat this Q&ASee also INSECT DAMAGE - WOOD REPAIR STEPS
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