bee biology

Molly’s bees: shot brood and laying workers

Thanks to everyone who participated in the diagnosis of Molly’s honey bee colony. Overall, I thought the answers were impressive—both thoughtful and nuanced. Many of you agreed with my own assessment of shot brood, but others mentioned issues I hadn’t even considered. It was a great learning experience for many, including myself.

I emailed my opinion to the owner and her friend before I decided to post the photos, so a couple people out there can vouch for what I’m saying.

The uncensored answer

I’m always in a hurry, often with dozens of pending comments to answer, so I tend to go as fast as I can. This time, I glanced at the photos and immediately concluded “inbred queen.” But later, I second-guessed myself. The more I looked at the photos, the more I wasn’t sure of what I was seeing.

I spend hours each week identifying bees on, and from that experience, I’ve learned how difficult it can be to evaluate a three-dimensional object in two dimensions. The same problem applied here. It was hard to tell if the cappings were flat like workers or mounded like drones, as many of you mentioned.

The shape of the nest

At any rate, when I first looked at the photos, I was pretty sure I was seeing at least some capped worker brood. Based on the overall shape of the brood nest—more or less football shaped with honey stored in the upper corners—I concluded that, at least for a while, the colony had a fertile, laying queen.

However, the shot brood pattern suggested inbreeding, meaning the queen was probably mated with close relatives. With bees, inbred queens yield what is called diploid drones—drones with two sets of chromosomes. They occur because what really determines the sex of bees is not the number of chromosomes but whether or not the genes at the sex locus are the same or different. Different forms of the same gene are called alleles, and healthy populations have a selection of alleles available for each gene.

When inbreeding occurs, there are fewer alleles in the mix, so any randomly selected pair of chromosomes has a higher probability of having two of the same allele at the sex locus. When the two sex alleles are the same, you get a drone with two sets of chromosomes instead of the usual one. (You can follow the above link for a more detailed explanation of sex determination in bees.)

Shot brood yields slow growth

More to the point, diploid drones do not reach adulthood. The worker bees detect their presence in the brood cell and pluck them out. The result is called shot brood, which is basically a normally-shaped nest with a bunch of “empties” scattered around. The more inbred the queen, the more empties you will see.

When you have a huge number of diploid drones, the queen will not be able to produce enough brood to maintain the colony. The colony population doesn’t grow so there are not enough bees to do all the work. This, I believe, was the initial problem in Molly’s colony.

What happened next

Please bear in mind that this was only a guess on my part. But assuming the hive was queenright, as least for a short time, what happened next?

From subsequent photos, it seems that laying workers took over the colony. The queen may have died, her pheromone levels may have been low, or she may have been an intercaste with assorted queenly deficiencies.

An intercaste queen is one that was raised from an older larva. Such queens don’t receive an exclusive diet of royal jelly from the get-go, so they are often small and only marginally competent to lead a colony. Although the workers replace intercastes quickly, they can sometimes provide an important bridge that keeps the colony alive. With any luck, the workers will build another queen from one of her eggs.

At any rate, that didn’t apply here and laying workers took over with a vengeance. Laying workers begin to develop after about three weeks of queenlessness, three weeks of insufficient queen pheromone, or the same length of time without open brood. In the next group of photos you can see eggs dropped into cells willy-nilly, all of which will develop into drones.

In summary, I believe that inbreeding caused the initial problem, but laying workers stepped in to finish it off.

The EFB question

Many of you raised the possibility of European foulbrood. I dismissed that idea, perhaps prematurely, because I have rarely seen EFB take over a colony from a package so quickly. Usually when I see it aggressively ravage a new installation, it came with a nuc rather than a package. That’s not to say it can’t happen, but I didn’t get that feeling in this case. Still, it’s a valid consideration because shot brood and EFB-infected brood can look amazingly similar. If you are unsure, testing for EFB would be the next step.

In the end

Ultimately, Molly combined her bees with a strong nuc, and it sounds like they are doing fine. Thanks to everyone for participating, and a special thanks to Molly for allowing us the opportunity.

Honey Bee Suite

Here you can see multiple eggs in some cells, a clear sign of laying workers. © Molly McMillion.

Here you can see multiple eggs in some cells, a probable sign of laying workers. © Molly McMillion.

The eggs look well-centered in some areas. It's possible that an ineffective or intercaste queen is still in the hive, but her pheromone levels are too low to stop the development of laying workers. © Molly McMillion.

The eggs look well-centered in some areas. It’s possible that an ineffective or intercaste queen is still in the hive, but her pheromone levels are too low to stop the development of laying workers. © Molly McMillion.

What looks like a queen cup was built among the laying-worker eggs. © Molly McMillion.

What looks like a queen cup was built among the laying-worker eggs. © Molly McMillion.

Multiple larvae are beginning to develop in some cells. © Molly McMillion.

Multiple larvae are beginning to develop in some cells. © Molly McMillion.


  • Hi Rusty

    As you probably know, multiple eggs is not a sure sign of laying workers. Eggs on the side walls of the cells, more probably laying worker. Multiple eggs can be a sign that the queen “wants” to lay more eggs but there aren’t enough nurses to care for them. She keeps laying the same cells o’er and o’er. New research calls into question whether a poor pattern is actually a sign of a poor queen. Perhaps you have seen it.

    Lee, Kathleen V., et al. “Is the Brood Pattern within a Honey Bee Colony a Reliable Indicator of Queen Quality?” Insects 10.1 (2019): 12.

    • Thanks, Pete, I will give it a read. In this case, however, a queen could not be located and no new worker brood appeared, so it is unlikely an over-eager queen was laying multiple eggs.

      But your point is well taken. In fact, it is the very reason I believe every situation needs to be examined on a case-by-case basis and the reason I like the “differential diagnosis” concept. It allows for the idea that several—or even many—different scenarios could cause the visible symptoms, so it’s helpful to list as many of those as possible, and them eliminate the ones you can.

  • Personally I would shy away from guessing laying workers in the original format of the hive in question- mainly because I did not see the kind of evidence I would want to be seeing to confirm laying workers and secondly because the colony was combined with a strong nuc and seems to now be doing well. Anyone who has tried to requeen a true laying worker colony will tell you it is never that easy. Laying worker colonies might contain dozens of laying workers- not just a single example as is found in a queenright colony, so the odds of a new queen suddenly appearing by introduction or combining, usually ends up with the laying workers having the upper hand by better numbers and the introduced queen usually gets the bullet. Too often we see failing queens, poorly mated queens, young mated fresh queens that lay multiple per cell early in their laying career, all written off as laying worker colonies as it is the easy conclusion to jump to.

    • Jeff,

      Combining with a queenright colony can work if the queenright colony is much bigger and stronger than the laying worker hive. The sheer size of the queenright colony can overwhelm the laying workers.

  • Rusty,

    You captioned of one of the photos as “What looks like a queen cup was built among the laying-worker eggs.” Will a colony make a “queen cell” out of a laying worker’s egg? if yes, does a drone develop in it?

    Thanks again for allowing your readers to participate in a little bit of what you do every day. It’s good practice for me too to consider all the possibilities (and learn some new ones)!

    SW Ohio

    • Alice,

      Queen cups don’t always lead to queen cells. The bees would know if a drone was developing in a queen cell, and they would then remove it.

  • You say that Molly combined the hive with a strong nuc. Did she dispose of all the nurse bees to stop the laying workers? Just curious. I’m a new bee and I heard that’s how you stop them, by dumping all the bees several hundred feet or more from the hive so only the foragers return home.

    • Marisol,

      She apparently just combined them and was successful. That’s risky, but sometimes it works, especially if the nuc was big and strong.

  • Rusty,

    Molly’s bees was a most interesting and educational idea. I thank you for the brilliant idea which gave us knowledge and insight, and much pleasure.

    I have one question – What is “shot brood”. Although you explain it a little it is not an expression I have heard before. I am assuming it is simply laying worker unfertilised eggs.

    • Michael,

      Shot brood is a term used to describe a brood pattern that has lots of holes, as if it were hit with a shotgun. Shot brood is usually caused by a poorly-mated queen, but it can be caused by EFB or even varroa mites.

  • Hi Rusty,

    Thank you for a very interesting subject too comment on. I have enjoyed reading all of the comments and replys. Thank you. I have learnt a lot from this.


  • Hi Rusty,

    Thanks for your website! As a second-year beekeeper in Colorado I have found the answer to many of my questions here. I started a second hive at the beginning of May. They are working hard and have drawn comb in 7 frames of the second deep. When I did my inspection today, it seemed like the larvae had an orange tint. (I don’t have a photo.) Nothing else seemed unusual. I have been feeding them 1:1 sugar water and I gave them a “pollen” patty when they were installed that does have an orange color. Some of the pollen has not been used. I am wondering if the orange tint is normal or a concern. Thanks for your help!

    • Susan,

      That is a new one on me. I suppose it could be related to the pollen supplement, but I don’t know that for a fact. Keep track of those bees, if you can, and see if development proceeds normally. It certainly is an interesting observation.

  • I am curious if I have a similar issue. I had to perform an emergency split earlier in the year and was forced to create a very weak, smaller hive in the process. I honestly did not think it would survive. After an agonizing wait, I checked back to find an existing colony, no eggs, but a few remnants of what I thought could have been queen cells. I gave it an appropriate amount of time and checked again to find new capped brood, larvae, and eggs but I could not find the queen. I couldn’t resist checking back on the health of the hive a week later. This time I found my queen walking around with new (but few – maybe 30 to 60 well-grouped) capped brood, larvae, and eggs…too many eggs – much of the hive was now filled with multiple eggs in each cell (some single, some double, some triple filled). My question is: could I have a functioning, mated queen working alongside laying workers and, if so, does my hive still have a good chance to function? It does have TONS of capped honey (from another hive) and pollen so there won’t be a food issue. The girls just need to grow up and start functioning properly while the queen refills the colony with proper people.

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