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Bees gathering fungal spores from sawdust?

Joey tastes sawdustOur honeybees were visiting my sawdust pile by the dozen yesterday, so I decided to see if I could track down what they were up to.  The internet was not very helpful --- several people reported seeing honeybees visit sawdust in the early spring when there's nothing else around to eat and they suggested that honeybees were collecting sawdust in lieu of pollen.  The sole piece of data backing up this assertion, though, seemed to be the coincidence that pollen is absent in the wild at this time of year and that this is the only season when people have noticed honeybees collecting sawdust.  While it's possible that honeybees could be tricked into thinking that sawdust is pollen (although at the bee scale, the two substances are orders of magnitude different in size, shape and texture), I suspect that bees who expend their precious winter energy on such a frivolous pursuit would die out in the wild.  Surely there's a better explanation.

Joey was visiting, and he suggested that the bees might be extracting some residual sap out of the sawdust.  We reached down amid our buzzing workers and snagged a pinch of sawdust apiece, then savored the dust.  At first, I couldn't taste anything at all, but after Joey's more discerning palate caught a hint of nutmeg, I thought that I might taste something too.  No proof there, but it made for an interesting photo.

As we continued to watch the honeybees, I became relatively convinced that they were putting something in their pollen baskets rather than sucking the liquid out of the sawdust.  I could see the insects using their legs to push at their pollen baskets, and none of the bees seemed to be sticking out their probosci.  The honeybees also seemed to be expending a lot of effort to kick through the pollen in search of their desired object --- by midafternoon, the pile of sawdust had turned from a volcano into a wide, squat hill.  Despite all this work, when I watched the bees returning to the hive, I couldn't see any sawdust in the pollen baskets, suggesting that the insects were collecting a much smaller substance than sawdust.

Bees visiting sawdustBack to the internet I went, this time delving into the scientific literature.  Several scientists repeated the pollen dearth maladaption hypothesis, but none cited any sources.  Instead, I was drawn to a series of articles by Dorothy Shaw, who reviewed over 100 years worth of reports on bees collecting fungal spores all over the world.  Most of the bees gathered spores from rusts or Neurospora, both of which have a protein content comparable to high quality pollen (around 25%).  Although in some cases bees seem to collect fungal spores when other foods are absent, other bees fly right past good pollen and nectar sources to gather fungal spores, returning to the hive with 100% spores in their pollen baskets.  Shaw suggests that the high protein content of the spores makes them a nutrition source comparable to pollen and that collecting spores can sometimes be a better use of a bee's time than gathering pollen since large masses of fungi allow the bees to fill their pollen baskets quite quickly.

I can't prove that our bees are picking through the sawdust in search of fungal spores, but I'm guessing that's the case.  If they're gathering rust spores, I might be able to test my hypothesis next time I look in the hive since scientists have been able to pick out rust spores stored in the brood chamber of honeybee hives by looking for their bright orange color.  I remember seeing bright orange "pollen" in our hives before, and now I wonder if I was actually seeing spores?

Our homemade chicken waterer takes the "yuck" factor out of backyard chicken care.

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Someone pointed me at this account in which "attacked a King Stropharia bed" that draws the same conclusion.
Comment by joey Sun Jan 30 11:27:26 2011
That's Paul Stamets' website, the king of fungi. :-) I'd read that in his book, which is why we planted Stropharia mushrooms this year (although they didn't do very well in our climate.) I wonder whether all of the reports of honeybees gathering "sawdust" on the internet might not really be reports of bees picking through the sawdust in search of fungi.
Comment by anna Sun Jan 30 15:18:13 2011

Great post - we were seeing the same behavior by our honeybees this week -- hundreds of bees visiting our sawdust stockpile. Yours seems the most likely explanation. Nice to benefit from all of your research on the subject! We are entering our 5th year of homesteading, looks like we're working on some similar projects....

Good luck to you and thanks again!

Comment by Milkweed Sun Jan 30 19:47:18 2011
Wow, I would never have guessed that bees visiting a sawdust pile involved looking for spores. Thanks for posting.
Comment by Zev Sun Jan 30 20:29:37 2011

Milkweed --- interesting to hear that your bees were doing the same thing this week. I wonder if a specific fungus is sporing right now?

Zev --- thanks for commenting!

Comment by anna Sun Jan 30 21:04:50 2011
Ana, ever the scientific mind. I like that you don't just believe what everyone else is saying just because everyone else is saying it. An untrue axiom may be repeated again and again, but that won't make it any more true.
Comment by Everett Sun Jan 30 23:17:02 2011
I think the adjectives you were really looking for, though, are "nitty picky" and "anal-retentive." :-)
Comment by anna Mon Jan 31 08:45:24 2011
I watched this precise behavior yesterday while moving sawdust mulch to the apple trees. The bees were expending so much energy fanning and kicking at the sawdust that they had to be after something. Last year when we mulched between veg beds with this sawdust, we saw numerous flushes of fruiting fungi.
Comment by Barbara Pleasant Tue Feb 22 10:41:33 2011
I'm glad I could clear up the mystery! I've enjoyed reading your articles in (I believe it was...) Mother Earth News, so I really appreciate you stopping by. (I can't quite remember where I read your articles, to be honest, but I remember visiting your website after finding out you're located in Virginia too.)
Comment by anna Tue Feb 22 10:44:51 2011

This website seems to think that they're gathering wood resin for propolis. . .

Comment by Dean Thu Mar 31 14:37:21 2011
Interesting hypothesis. My understanding is that bees gather resin that oozes out of trees like pines to make propolis, and this wood is not a softwood and lacks that resin. (It's usually a bad idea to burn pine in a wood stove for that very reason.) But most of our lumber is pine, so I could see how they could come to that sawdust to get resin --- maybe we have two different foraging behaviors going on depending on what kind of wood we're cutting.
Comment by anna Thu Mar 31 16:23:59 2011
I think the only way to know for sure is to have it tested... If it is fungus spores, I think there's sawdust mixed in as well as it had that kind of texture on their baskets... I saw my bees bringing in saw dust earlier today in my observation hive and they even went as far as to pack it into cells...They also danced to tell others about it...
Comment by Anonymous Tue Jan 3 21:24:52 2012
Yeah, quite possibly they were getting some sawdust too. On the other hand, they did seem to be very choosy --- not just grabbing the sawdust on top by working their way through it in search of what they wanted.
Comment by anna Wed Jan 4 09:39:04 2012
Wood decay fungi grow in sawdust piles and degrade the cellulose (one of the main components of wood) into sugar (glucose). This can accumulate faster than the fungus uses it. It seems to me that the bees might be using this sugar.
Comment by David Boyle Fri Jan 4 13:22:31 2013
The last couple days I have been milling a dead ash tree... Sawdust mixed with water made àn almost sand like powder of sawdust... I noticed several which i believed to be honey bees... They flew all around me collecting this wood powder mix... They defiantly are not aggressive.. They worked right along with me... Also there were some wasps but very few in comparison to the honey bees.. I'm glad I found this post.. Today I will try and find their hive.. I'm excited to know for sure if they are true honey bees.. The internet has not been much help on what honey bees eat... Just says they and collect pollen so what in the heck are these honey bees up to...??
Comment by Damian Taucher Thu Aug 28 09:52:35 2014
My husband runs a portable sawmill.He mentioned that he saw honey bees working the sawdust. We were wondering we know.
Comment by Debbie Cretsinger Mon Mar 9 00:42:01 2015
WE found hundreds of honeybees in our sawdust pile this morning and they hung out until suppertime. I too wondered what in the heck they were after and my husband thought similarly to you that they were collecting residual sap. I don't know about yours but ours almost seemed to be drunk; not just picking up flecks of sawdust but cuddling it and doing tumblesalts and diving headfirst into it digging with their legs to push themselves in further. It was quite a sight! We assumed that they might be terribly hungry after the long winter we had and offered them some sugar syrup. Many of them did go after it but even they appeared to act drunk. They were wrestling with each other in the shallow sap like mud wrestlers and wandering aimlessly around like drunken soldiers. They are not in any way aggressive, they don't even notice us moving the tarp around or squatting down to get close. They even landed on us a few times just to visit a second and fly off. I too searched the internet looking for a reason for this and yours is the only site I found that makes any sense. Thanks for posting!
Comment by Norma Paisley-Moore Mon Apr 6 17:10:36 2015
About a week ago I cut down a dead standing ash tree that was killed by the Emerald Ash Borer. When I cut the tree up for firewood I left a large amount of sawdust on the ground. For the last week my honeybees have been rolling all through it. I thought maybe the bar oil from my chainsaw was attracting them to the wood chips since there is very little pollen to be found right now. The funny thing is that there are 2 Maple trees right there in full bud and I haven't seen a bee on them. I never heard of honeybees gathering fungal spores. This was very informative. I will have to observe them a little closer next time. Thanks.
Comment by Anonymous Tue Apr 7 17:50:07 2015
Hi from New Zealand. We had bees swarm over our house yesterday for several hours. They weren't aggressive towards us but seemed energetic and in search of something. We assumed they were looking for a new home but I had a middle-of-the-night-thought that there might be another reason and my hypothesis was that they might have been attracted to spores from musty clothes that were hung outside to air in the sun after a spring clean. After reading your article and comments I wonder weather an old decayed log that I put a spade through and broke open the day before (and combined with a hot dry wind) could also have triggered it?
Comment by tom Thu Jan 5 10:45:25 2017