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The Classroom

The Classroom – April 2020

- April 1, 2020 - Jamie Ellis (excerpt)

The Classroom - ABJ - Jamie Ellis

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Q The Crud

What is the best course of action for crud as far as treating the colony and re-using the comb?

Thank you
Eric Joswig
Florida, December



First, let me define the “crud” briefly for the reader. The crud is a general name given to a condition associated with bee brood. Colonies showing signs of the crud often have spotty patterns, uncapped brood cells that should be capped, dead or dying larvae and/or pupae, brood “melting” in their cells (I will call this “melty larvae”), etc. Some people also call this “snot brood” or other interesting terms.

There are a few things to know regarding the crud. First, we do not know what causes it. Without that information, it is very difficult to make management recommendations. Interestingly, I had a look at some crud colonies a few years ago and found European foulbrood (EFB) present in high levels. A Canadian colleague of mine reported the same thing at the time. Recently, I spoke to Dr. Meghan Milbrath (Michigan State University) who knows a lot about EFB and the crud. She suggested that there is a strong correlation between the two. She shared that she tested samples from many hives that had crud-like larvae (sunken capped brood, melty larvae), and they all tested positive for EFB. Often times, the same colony would have some larvae that looked crud-like, and some larvae that looked like classic EFB.

It is possible that the crud is a modified manifestation of EFB. It is also possible that the crud occurs when EFB manifests as a secondary infection, perhaps after a viral infection. You often hear beekeepers report that the crud manifests about the same time every year. Dr. Milbrath even noted the same thing, saying her beekeepers often see it after coming out of pollinating blueberries early in the year. I am not saying that blueberries are the cause, only that something routinely seems to be the trigger for the crud at that time of year.

To me, what many beekeepers call the crud can look like parasitic mite syndrome, which is just a fancy way of saying general brood stress due to Varroa and the viruses they carry. If this is the case, the crud would be best controlled by managing Varroa. Dr. Milbrath feels that the crud produces more distinct signs of infection than those produced by parasitic mite syndrome. Parasitic mite syndrome and the crud overlap in their melty larvae, but a colony with parasitic mite syndrome will often have bees that are dying on emergence from the cell (not seen in crud), and it often occurs later in the season as Varroa populations grow. The crud usually occurs early in the year and can be found in colonies where Varroa populations have been carefully controlled.

Nevertheless, until we know what it is, and what causes it, it is difficult to make specific recommendations for its control. I tend to tell beekeepers whose colonies have it to make sure their bees have adequate nutritional resources. Some beekeepers also suggest that it seems to disappear on its own when major nectar flows start. Many commercial beekeepers with whom I discuss this note that it often clears up after colony treatment with antibiotics. Dr. Milbrath agrees. A veterinarian can write a prescription for oxytetracycline for a hive that has the crud. If it is EFB-related, then it should subside with antibiotic use. Feeding the colony and use of a shook swarm is often good practice for brood disease in general, even if the cause is unknown.

How does one clean combs from colonies showing signs of the crud? Again, it is hard to answer this question given we do not know the cause. However, when in doubt, get rid of any combs that contain dead or diseased brood. It is possible that irradiation will sterilize the combs and this could help, but only if the crud is caused by a pathogen.

All that said, we desperately need to study this brood condition, determine its cause, and develop management strategies to address it. Thanks for bringing it to the attention of the American Bee Journal readership.

[This answer was reviewed and edited by Dr. Milbrath. I wanted to note her contribution and thank her for her valuable insight.]

Q Are Tracheal Mites a Threat?

 I had an interesting conversation with a friend and we were wondering if tracheal mites play into parasitic mite syndrome, or is it a standalone problem of its own? Do you have any recommendations about treatments for tracheal mites? We were looking for grease patties, but not happy with the information we found.

Debbie Martin
West Virginia, January


I do not think that tracheal mites are a big problem any longer. Parasitic mite syndrome is exclusively related to Varroa and its virus complex. I think the things we do to control Varroa work pretty good against tracheal mites as well. If, though, you are worried about them (and I do not think you should be), I think that grease patties are the way to go. You mix vegetable oil and powdered sugar together until you get a Play-doh type consistency. You place a pancake-sized patty of this mixture on top of the brood chamber. I think this works as well as anything and it can be applied to your colonies at any time of the year.

It is funny: I once saw tracheal mites quite a bit when I worked in Georgia. However, I have never seen a tracheal mite positive sample since I have been in Florida. I do not hear talks about them, neither do I see research on tracheal mites. I get the impression that most beekeepers and scientists do not feel they are a significant threat any longer.

There are good online resources for conducting a tracheal mite dissection of bee samples. You would need a dissecting microscope and some basic tools. However, the technique is not that difficult to learn. My team and I developed a guide on the method. See: Likewise, you can find it by Googling “EDIS tracheal mite dissection.”

Q  What happens to Varroa in a dead hive?

What happens to the Varroa in a deadout hive? How long can they live on, sucking on the fat bodies of dead bees? How long do Varroa live? In a mild winter, can they survive to the spring, living off dead bees? Can they survive a light freeze? If this has not yet been researched, is there a place to post such questions, as suggestions to future grad students?

Charles Breinig
Pennsylvania, January


Your questions are the subject of active research projects in a few laboratories around the world. I will answer what I know and then throw in a healthy dose of speculation. Just be aware that the scientific community’s thoughts on this topic are evolving … even as I write my response.

First, I suspect a large number of Varroa in a deadout hive simply die. Parasites have a hard time living without their host, especially a parasite tied to its host as closely as the Varroa is tied to the honey bee. That said, it is known that there is quite a bit of Varroa dispersal from a colony that is in the process of dying. How does this happen? It likely occurs through robbing (bees from strong colonies rob the Varroa-sick ones) and drifting (Varroa-sick bees drift to healthy colonies). Both of these contribute to what a lot of people are beginning to call the “Varroa bomb.” This is just a fancy way of saying that Varroa from sick-and-dying colonies seem to distribute quickly to neighboring colonies, almost like a Varroa explosion.

I did a few quick searches and could not find any evidence that Varroa feed on dead bees. This does not mean that they do not feed on dead bees. It only means that it has not been studied, or at least studied in detail. Someone in my laboratory is currently looking at Varroa longevity on dead adult and pupal bees (your questions are serendipitous). His preliminary data suggest that they can survive around five or so days on dead adult bees and a little longer on pupae (he said 7-10 days). So, it seems possible, but my guess is that dead bees are not an important food source for Varroa in the field.

We do know that Varroa can survive on adult bees for a few months. I have not seen data on the maximum longevity of Varroa, but they do survive winter on adult bees. I do not think it is realistic to expect them to survive winter feeding exclusively on dead bees. I also do not think they can survive a freeze of any type unless they are on bees engaged in an active cluster.

How do you get your questions to prospective graduate students? You can post questions like these on some of the online beekeeper listservs. You also can post comments such as these to the social media accounts of various bee research laboratories. For example, you can post it to my team’s sites: @ufhoneybeelab. Finally, your questions are making it into the American Bee Journal and hopefully a lot of students will see them this way☺. Again, these are great questions and really have my wheels spinning. Thanks for asking.

Q Welcome Aboard!

 I read your letter of introduction to the Classroom in the January ABJ edition. Although I was sad to see Jerry Hayes leave, his guidance and knowledge are very valued, I’m pleased that someone of your caliber is taking his place. Over the years I’ve read a number of your articles in the ABJ and have always received a lot from them. I recently shared your Oct 2017 article on the Indispensable Nuc with our bee club. So, congratulations on your new role, I look forward to your commentary and wisdom, and am sure you are going to do fantastic!

David Williams
Washington, January


Wow, thanks David! I appreciate your support and am glad you are a regular reader of the Classroom. Also, I am glad the nuc article is of value to you and your beekeepers. For the readers, the article can be found by Googling “EDIS nuc honey bee.” It is entitled “Using Nucs in Beekeeping Operations.” Other resources my team and I produce can be found by visiting and clicking on “beekeeper resources.” Thanks again!

Q Locally Adapted Queens

 There seems to be a common notion that raising honeybees over successive generations in a particular locale will, over time, result in “locally adapted queens” that will outperform queens imported from other places. I am not speaking of selective breeding programs (Buckfast, Saskatraz, or those described by Randy Oliver, Lawrence Conner and others), in which specific characteristics are rigorously evaluated and carefully chosen…