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Counting the dead bees

You stroll past your hive for a quick peek and are dismayed to find five dead bees on the landing board. What does that mean? Is your hive in trouble? What should you do?

I can’t stress this enough: five dead bees is nothing. Nothing. The only difference between those five and a thousand of their sisters, is they happened to fall on the landing board. You aren’t worried about the other thousand because they fell somewhere else, a place where you can’t see them or count them.

I’ve read many estimates for the number of bees that die daily during foraging season, but depending on the size of the colony and local conditions, the real number is probably between 800 to 1200. For the sake of argument, I’m going to say 1000, which I think is a reasonable number.

The average lifespan of a worker bee

The first thing to consider is the average lifespan of an adult worker bee. For a healthy worker when all is going well, that lifespan is somewhere around 4 to 6 weeks. The period begins when the bee emerges from her brood cell and ends when she dies of old age or misadventure.

Old age is self explanatory and is often expressed by worn wings and hairless bodies. Misadventure can be due to anything, such as tangling with a spider web, getting blown away by the wind or smashed by a car, or getting diced by a lawn mower. As we humans say, stuff happens.

It turns out that four to six weeks is the number commonly cited for the average adult lifespan of most bees. That includes your mason bees, leafcutters, sweat bees, and miners. Basically, that’s how long bees working in the field live. The native bees emerge from their nests in spring and spend the next four to six weeks building a nest and laying eggs. They continue building until they die, and their offspring remain in the nest until the following year.

So in regard to an individual’s lifespan, honey bees are not unique. What is unique about honey bees is their ability to raise “winter bees” also know as diutinus or long-lasting bees. These bees are the ones that live inside the nest, survive the winter, and kickstart the colony the following spring. But that is another subject.

The egg-laying machine

The second thing to consider in a normal colony is the egg-laying ability of the queen. This number also varies, and I’ve read estimates that range from 1000 to 3000 eggs per day. To raise this many eggs, the colony needs a large force of healthy workers. Even so, we’re talking about a lot of eggs. Let’s take an average estimate of 2000 eggs per day during peak season.

Now, not all the eggs will grow into viable adults. Some will die at each stage of development. Let’s be conservative and say 80% reach adulthood. That’s .8 x 2000 or 1600 newly-hatched bees per day. If 1000 adults die during that one-day period, you still have a net gain of 600 bees. At the end of a month you have 600 x 30 or 18,000 more bees than you started with, even with losing 1000 per day. If 90% reach adulthood, you get 24,000 extra bees by the end of a month, which equals a good size swarm.

Yes, these are estimates based on averages, but they paint a picture. If you didn’t have all those bees dying each and every day, things would soon be out of control. If you took 90% of 2000 x 30 without deleting the dead ones, you’d have 54,000 additional bees at the end of a month—another whole colony. At the end of six months, you would have seven full-sized colonies. But it doesn’t work that way.

My point in reviewing the numbers is to illustrate that the daily loss of bees is much greater that we realize. The fact that we don’t see the dead, coupled with enormous amounts of brood rearing, lulls us into thinking that bees don’t die. In fact, nothing could be further from the truth.

Rusty
Honey Bee Suite

Bee-on-squash-leaf
Like most adult bees, a healthy honey bee worker lives about four to six weeks in the spring and summer months. © Rusty Burlew.

Mason bees in a honey bee hive

Mason bees, leafcutting bees, and other cavity nesters are incredibly easy to please. The hype you hear about their tubes needing to be a specific diameter, or a special length, or placed in a particular location is mostly nonsense. Left alone in the wild (as they were for millennia) the bees find all types of cavities that please them, from beetle borings to woodpecker holes to hollow reeds. In the wild no one measures the diameter, cuts them to length, or holds them parallel to the ground. We humans can be terribly self-important.

But just like everyone else I have neat rows of little tubes—paper straws in empty vegetable tins—and the bees certainly use them. A tin full of straws takes about three days to fill at the height of orchard bee season. These early bees are followed by other types of masons and leafcutting bees, all angling for a spot in a green bean can. Luckily for them, my dog eats a can of green beans each and every day, so when a can fills up I simply pull it off the bee shelf and add another.

But the bees in the straws are the tip of the iceberg. These are the gregarious masons that like to live (it seems) on the same block as everyone else. Other individuals nest to a different drummer.

A couple weeks ago I was checking my honey bees when I noticed mason bees flying in and out of an empty hive that was sitting between two very active colonies on the edge of the woods. You wouldn’t think mason bees would go there, with the air teaming with pheromones and threatening sounds. Curious, I opened the hive and found masons actively building away. What cavities were they using? Brood comb, of course. If you think straws in a can are tightly packed, you ought to take a good look at an empty brood comb. Claustrophobia big time.

Seeing these nests reminded me that I had a section box from the previous year that held some mud nests. I went to check on the section box, which I had put outside a month ago, and sure enough two of the bees, Osmia aglaia, had already emerged. These bees, sometimes called berry bees, are active later in the season and reach their peak after the orchard masons are done for the year.

Many species of bee in the family Megachilidae nest in empty tubes and tunnels, so it is not too late to put out your cans and paper straws. Get a dog with a green bean fetish and you can keep filling cans all summer long.

Rusty
Honey Bee Suite

This brood frame was inside an empty bee hive. © Rusty Burlew.
This brood frame was inside an empty bee hive. © Rusty Burlew.
Mason bees at work in a brood frame. © Rusty Burlew.
Two Osmia lignaria at work in a brood frame. © Rusty Burlew.
Mason bees living in a section frame. © Rusty Burlew.
Osmia aglaia nests in a section honey frame. I have no idea why they all like the upper left-hand corner. © Rusty Burlew.
Plenty of paper straws. A can fill up in about three days. © Rusty Burlew.
Plenty of paper straw nests. A can fills up in about three days and then I replace it with a new one. © Rusty Burlew.

Absconding bees or death by Varroa?

This past fall, I received many reports and questions about absconding bees, perhaps fifty in all. Every year I get these and I must admit that I’ve always taken the beekeepers’ word for it when they said their bees absconded.

But this year I realized the sheer number of reports was off-kilter somehow. Yes, honey bees abscond on occasion, but it is rare, and it is usually the result of untenable conditions in the hive.

Absconding due to thymol

Only twice have I seen absconding myself. The first time was in the middle of a treatment with thymol (Apilife var) for Varroa mites. I found the cluster, along with their marked queen, in a nearby cedar tree where I was able to capture them. With a bit of research, I discovered other beekeepers who had similar experiences with thymol, especially when daytime temperatures spiked above the recommended treatment threshold.

Absconding due to scavengers

The second time one of my colonies absconded, I received a call from the landowner where I kept an outyard. She said yellowjackets were going in and out of one of my hives. By the time I got there, the bees were pouring out of the hive and clustering below the hive stand, queen and all. I was able to drop the cluster in an empty hive where it stayed. When I opened the original hive, I found it teeming with yellowjackets, bee bits, and ripped and dripping combs.

Other beekeepers have reported absconding after severe infestations with wax moths and small hive beetles. But in all three of these cases, the proximate cause was a scavenger, which means the colony was weak to start with. A healthy, vibrant colony is generally able to control attacks of yellowjackets, beetles, and wax moths. A weakened or hungry colony, however, may decide it is losing the battle and opt to leave. At least, this is how it appears.

Not absconding, but something else

The vast majority of the reports I heard this fall appeared not to be the result of mite treatments or scavengers. Instead, the stories, nearly identical in all cases, claimed the following:

  • The colony that “absconded” was the largest in the apiary, or one of the largest.
  • The incident occurred in September, October, or November.
  • The colony seemed normal during a recent inspection, usually between one and four weeks prior, and then suddenly disappeared.
  • The beekeeper did not see the bees leave or find them later.
  • Honey was left in the hive or it had clearly been robbed (as evidenced by ripped cells).
  • A small amount of brood remained in the hive.
  • A small number of listless bees lingered on the combs, but the rest were gone.
  • The queen was missing.

At first, I wondered if an influx of Africanized genes into the larger population was causing an increase in absconding, but I could find no evidence for that theory in recent literature. So I spent considerable time re-reading the reports (at least those I could find) and concluded that nothing about them suggested absconding. Instead, the observations listed are classic signs of collapse due to Varroa mites.

A plethora of non-treatments

Where I could, I went back and asked those beekeepers how they treated for mites and when. The answers were a hodgepodge, but some examples are listed below:

  • I didn’t see any mites so I didn’t treat
  • I dusted with powdered sugar in the spring and fall
  • I used Honey-B-Healthy
  • I used wintergreen patties
  • I bought a local queen
  • I have a screened bottom board

While there is nothing wrong with doing these things, none of them—even in combination—will handle a mite problem. Many different philosophies have evolved for raising bees in the world of Varroa, but learning to recognize an infestation seems like a logical first step.

Often, when I suggest a colony disappeared due to Varroa mites instead of absconding, I am roundly trounced. “No, they were fine last week.” “It’s not possible because it was my strongest colony.” “The colony was new this year, so it couldn’t have mites.” I find it intimidating to say anything.

What we know about Varroa collapse

Based on observations going back many years, beekeepers collectively know a lot about collapse due to Varroa. Some key points:

  • The number of mites in a colony increases as the bee population increases. But when the bee population begins to decrease in the fall, you are faced with more mites per bee. Likewise, when drone production stops, the mites move into the worker brood. This is the reason colony death from mites skyrockets in September, October, and November.
  • Large colonies support huge numbers of mites. When these colonies contract in preparation for winter, the number of mites in the hive is astronomical. Large colonies—even those that appear healthy—are often the first to fail due to the sheer number of mites.
  • Not only do the large ones fail, but they fail fast. Some say that a large colony can collapse within a week. This “here today, gone tomorrow” aspect is what leads beekeepers to think their hive absconded.
  • Oddly enough, sometimes smaller colonies do better against mites. Their smallness may have been caused by swarming, queen supersedure, or splitting, all of which produces a brood break sometime in the season, which means less brood was raised and fewer mites were produced.
  • Colonies that have collapsed from mites often leave behind honey, sometimes large amounts. This is especially obvious when the colonies collapse during cold months when predators are less likely to clean out the combs.
  • Colonies that collapsed from mites often leave behind some brood. This occurs because life in the hive was preceding normally until a large influx of mites took them down. Because it happens so fast, it can easily occur within the 21-day brood cycle. The result is a patch of brood in an otherwise empty hive.
  • The queen may be missing for a number of reasons. She may have been infected with viruses and died, or she may have starved, or she may have died of exposure because her work force is gone. Her body may have been removed from the hive or she could have fallen into the hive debris. A dead and shriveled queen is hard to spot in a pile of bee bodies.

Where the bees go has always puzzled me, but there have been many observations:

  • In the beginning, the live bees drag out as many bodies as possible. This is more obvious in poor weather when they leave them just outside the door. During warmer or drier days, they will fly them further away so the dead go unnoticed.
  • Sick bees will often fly out and die for the good of the colony. Many people have observed this behavior. On cursory inspection, the dying bees look fine, but they are not.
  • When the hive is sufficiently weakened, predators and scavengers may move in. This can give the appearance that they are the cause of the problem when, if fact, they are the result of it.
  • Sometimes bees have been seen to “abscond” but not in a coordinated way. Instead, individuals may flee from the colony and take up residence in a nearby hive. This drifting spreads mites to other colonies.

I don’t know why beekeepers are unwilling to believe or admit their bees died of mites. If I suggest any other cause of death, they are likely to accept it—or at least consider it. But mention mites, and the answer is usually a resounding “No way!” A stigma associated with mites suggests that you are somehow lacking in ability as a beekeeper if you lose a battle with Varroa mites.

Another common misconception is that mites are easily visible by the beekeeper. In fact, mites make a point of hiding from view. They spend a lot of time beneath capped brood cells and are rarely seen on adult bees. Even if phoretic mites are present on the adults, they can can remain partially concealed between segments.

Whatever the reason for dismissing the mite problem, it’s sad because by denying the evidence we preclude an opportunity to learn and improve. Like most conundrums, the more you know, the more successful you will be.

What to look for

I would prefer you didn’t take my word for it, but do a postmortem on the hive that you suspected of absconding. The first clues to death by Varroa are listed above, that is, a suddenly empty hive that still contains honey and a patch of brood. But if you want more evidence, here are some other things to look for:

  • Look for guanine deposits inside the brood cells. These are white, crystalline patches that adhere to the top of the cell. Randy Oliver at Scientific Beekeeping has a nice description.
  • If there is capped brood, open the cells, pull out the pupae and look for varroa mites.
  • Sift through the debris on the bottom board and search for dead mites.

While honey bees will abscond on occasion, it is rare, especially in races of the European honey bee such as Apis mellifera ligustica and A.m.carnica. Before chalking up your lost colony to something that rarely happens, do a thorough postmortem on your empty hive and keep an open mind.

Rusty
HoneyBeeSuite

Asconding-colony-2 under hive stand
This colony left the hive (above) that was full of yellowjackets. The cluster is small because many had been killed by the wasps. © Rusty Burlew.
Absconding-colony-1 hanging from hive stand
Once I relocated the colony into a new hive, I found that the queen was with them. No living bees remained in the hive, only parts of dead ones and ravaged combs. © Rusty Burlew.