After finding that a robbing screen can frustrate bees returning to their own hive enough to cause them to “give up,” I now wondered to what extent a screen could thwart potential robbers investigating the scent coming out of a hive. But first, let’s look into the details of how robbing takes place.

Fact-checking some “common knowledge” about Robbing behavior

Let’s fact check some “common knowledge” regarding robbing [[1]]:

Claim: Robbers appear to seek out weak…colonies with a vengeance…

Fact: There’s no evidence that robbers “seek out” weak colonies (but they do tend to be chased away by the guard bees of strong colonies). And the colorful term “vengeance” (punishment inflicted or retribution exacted for an injury or wrong) is a human attribute, not relevant to honey bees. Robbing bees are only interested in obtaining sugar with the least amount of effort.

Claim: …and will not hesitate to kill the bees within in their determination to steal whatever honey is available.

Fact: Robbing aren’t looking to pick a fight, and although they may shove each other to get to the honey, they go out of their way to avoid conflict. As mentioned in my previous article, robbers don’t bother or harm any nondefensive bees in the hive being robbed.

Claim: Robbing bees exhibit a nervous behavior that is quite unlike that seen under any other circumstances.

Fact: There’s a difference between “nervous” and cautious. I’ll investigate whether this behavior is actually unique later in this article.

Claim: One popular blog wrote: During the course of robbing, the bees turn frenzied and aggressive – both towards each other as well as to any nearby people. Stinging increases.

Fact: From what I’ve observed, robbing bees may get pushy, but are hardly “aggressive.” Any aggressive bees would be the alarmed guards of the colony getting robbed (who may sting a human standing nearby), but the robbers themselves have zero inclination to sting.

Many years ago I read an article in which a prominent East Coast beekeeper wrote about how he’d take a truckload of extracted supers out to his apiary to allow his bees to “rob out” the honey. He related that on hot days, he would strip down to his BVDs and happily stand in the middle of the cloud of robbers, who displayed no interest in stinging.

I’ve myself worked in the middle of clouds of “robbing” bees that were so dense that it was difficult to take a breath without inhaling a bee (I don’t even bother to put on a veil). But such bees had no inclination whatsoever to sting me or the other bees that they were so vigorously shoving against (Figure 1).

Fig. 1 Rose is here amusedly demonstrating that “robber” bees vigorously competing to feed on scented syrup have no more inclination to sting than do foragers on attractive flowers.

Anthropomorphizing bee behaviors

In my last article I warned against our tendency to anthropomorphize bee behaviors. The reality is that honey bees sensorially perceive the world entirely differently than do humans. Although capable of thought and learning, their tiny brains have limited capacity for deep analysis and thinking, much less human concepts of morality. By happenstance while writing this article, I came across a piece published in this Journal in 1966 by one of my icons — Dr. Norm Gary — entitled Robbing Behavior in the Honey Bee (read it at [[2]]). In it, he writes:

Thus, we mistakenly attribute many human virtues to honey bees. Instead of referring to robbing as a special type of foraging activity, we call it “robbing.” Immediately a false impression is created. The implication is that robber bees have a criminal nature and knowingly steal honey that doesn’t belong to them. Some authors mention that robbers may be distinguished by an air of roguery and a nervous and guilty agitation as they hover in front of the colony that is being robbed. The implication is clear –– bees know right from wrong –– otherwise, why would they act nervous and guilty?

Dr. Gary concludes that:

ROBBING IS SIMPLY A NORMAL FORAGING PROCESS THAT MAY BE EXPLAINED IN TERMS OF KNOWN FORAGING BEHAVIOR.

From the evolutionary standpoint, it is extremely unlikely that a special robbing behavior, distinct from normal foraging behavior, could have evolved, because colonies were sparse in nature, nectar was abundant, and exposed unguarded honey was a very rare occurrence.

Since that writing, there has been more research on “conspecific cleptobiosis” (stealing food from another member of your species). In a number of species of food-caching animals, reciprocal pilfering is the norm [[3]] –– this is certainly the case for honey bees.

Practical application: Such pilfering behavior, although abhorrent to us, may actually be of benefit of a breeding population, since it allows for the quick transfer of hard-won sugar reserves from failing colonies to any related survivors in the neighborhood, before that precious honey gets consumed by ants or other species of predators or scavengers. This trait is especially evident with bees carrying African genetics, who plunder other hives with abandon.

When we place a bunch of hives in unnaturally close proximity to each other in an apiary (which creates a goodly amount of “drifting” of bees from hive to hive), foragers routinely help themselves to inadequately-unguarded nectar or honey from the larders of other colonies, via progressive or overt robbing.

There are different types of foragers

The last behavioral stage in a worker bee’s life is that of foraging –– a task that it will typically engage in until it “wears itself out” after about two weeks of effort. But as we often find with honey bee biology, it’s a bit more complicated, since individual workers have different aptitudes for learning, thinking, and leadership, which can lead different individual (albeit short) “careers.” Dr. Tom Seeley graciously granted me permission to share a great diagram of his on forager dynamics (Figure 2).

Fig. 2 With experience, a novice forager can progress to being an investigating scout, or an inspector (a forager who continues to return to check back on a previous source of nectar). “Reticent” foragers wait on the combs for scouts, inspectors, or excited returning foragers to “reactivate” them. Robbing is initiated by a returning scout who has discovered unprotected honey, who then recruits a mob of foragers into employment. Chart also in [[4]].

Be in awe: The honey bee has evolved a complex management system to most effectively allocate the field force of the colony for the greatest productivity and returns on investment.

Persistence of Memory

Karl von Frisch (the discoverer of the waggle dance) wrote about “inspector” bees back in 1923 [[5]]. Inspector bees are foragers who have “retired” from a food source that has become depleted, but continue to occasionally check back to see if it’s again available (if so, they’ll resume foraging on it and recruit others). Moore [[6]] elaborated on this behavior in 2011, using the oh-so-scientific term “food-anticipatory activity,” (which of course has a handy acronym: FAA):

The environment surrounding the honey bee colony is constantly changing: on any given day, some plants come into flower while others become depleted. After a period of rain, some depleted plants may recover their ability to yield nectar. Rather than depending on the flower patch being discovered again by scouts, the prolonged FAA (at least in some individuals) would ensure that the source receives significant reconnaissance.

Practical observations: The forager force of a colony doesn’t waste energy or muscle wear on fruitless foraging. In the dense bloom of an almond orchard, there may be zero bee flight once all the pollen has been gathered (often by noon). First thing the next morning, the inspectors fly out to see whether they should tell the inactivated foragers (and any novice recruits) to resume foraging, while scouts scour the landscape for new finds. At home I’ve been observing this on a coyote brush shrub along my driveway (which appears to refill its blossoms with nectar at night) –– early in the morning, a few inspectors show up and return to their hives; within minutes the plant’s blossoms are roaring with bees. But by 10:00 am there are only a few, and by noon the bush is abandoned, only to be roaring again the next morning.

The forager force of a hive can be considered to be “on call,” since it can rapidly shift from one nectar source to a more “profitable” one –– such as unguarded combs of honey [[7]].

Practical application: This simple, but well-coordinated, work allotment strategy directs the forager force to the best returns on investment, while allowing them to save their energy (and prolong their lives) when resources are scarce or intermittent.

How robbing happens –– Step by Step

Scouting forager bees continually investigate sources of odor that they associate with a potential sugary reward (commonly from a nectar that their colony has been recently gathering) [[8]]. If that scent happens to be emanating from a dark cavity (as opposed to an open flower in the sun), the forager will (understandably} cautiously approach the entrance, not only to figure out where the odor is emanating from, but also to determine whether there are competitors or defenders present, or predators lying in wait.

If there are responsive guard bees at a cavity entrance (or competitor species or spiders on a flower), the scout will back off and fly away; but if it instead is able to walk in and come out full of nectar, game on! The scout, now with its crop full of easy pickin’s, will return home, and by performing vigorous waggle dances, recruit additional foragers (now considered as potential “robbers”). And if those recruits also subsequently manage to get past the guards and successfully return home, the number of additional recruits can increase exponentially within minutes (easy to observe by leaving a comb of honey or spilled syrup exposed during a dearth).

Practical questions: No mass robbing will take place unless a scout, forager, or inspector first returns with a prize. The mission of the guards is to prevent this from happening. Beekeepers commonly help the guards by reducing the size of the hive entrance. But will the barrier of a robbing screen also thwart investigating scouts? And perhaps more importantly, deter any recruited additional foragers?

Once the robbers have plundered the sugar source, there is no longer any return on investment for returning to the site, and the robbed hive or comb is just as quickly abandoned. But not completely abandoned –– some inspector foragers will continue to return to the scene of the crime (and nose around the neighborhood) for several days, sniffing for the scent associated with the sugary reward (easy to observe if you put a net over combs being robbed).

Importance of Scent

Forager bees identify and investigate potential floral sources by color (notably blue, yellow, and ultraviolet), and by shape and pattern, but especially by scent (which plants produce specifically to attract pollinators). It’s very clear to me that robbing is all about scent:

Practical observation: Just this week I picked up a deadout nuc in the middle of my crowded home apiary during a dearth, during which not only were there plenty of bees robbing at the honey house and at our feeder jar filling station, but also where we were intentionally inciting robbing by putting out scented syrup for our experiments. Yet even after sitting open in a line of nucs for at least a week, the combs of that deadout nuc were still full of open honey that hadn’t been robbed –– that honey apparently did not have the scent that any scouts had been trained to.

To again quote from Norm Gary:

It is known that the newly recruited bee has received rather precise information about the food, that is, its odor, flavor, distance, and direction from the colony. If the food is close to the hive…the directional component of the “message” in the dance is very weak, or non-existent. Consequently, the recruit bees fly in all directions within approximately a 50-yard radius, as they search for [the scent].

Compared to the ignored honey in the deadout nuc, we easily trained foragers from colonies to seek out scented syrup. If we simply put a couple of drops of scented syrup on the landing boards of several hives in the apiary , within a few minutes investigating scouts would show up at a tray of scented syrup placed anywhere on the property. They would tank up and leave, and soon the tray would be covered with bees –– apparently foragers recruited to the scent by a returned scout (Figure 3).

Fig. 3 It’s easy as pie to train foragers to scented sugar syrup. Note the shiny abdomens of several of the bees –– in the sticky hustle and bustle of mass feeding (robbing), those foragers often get the fuzz rubbed off their bodies (and visually stand out on the combs).

Practical application: As opposed to bees afflicted with Chronic Bee Paralysis Virus, their wings are not chewed, and they don’t tremble. But their presence does indicate that the colony had recently engaged in robbing, meaning that its foragers may have carried back pathogens or mites from the robbed hive, or from the other robbers that they mingled with.

Our initial experiments to test the deterrance effect of screens

It occurred to me that since robbing is initiated by a scout successfully entering a hive to plunder, then we could best test the efficacy of a screen design without the presence of guard bees or honey combs (since this would eliminate the variables of colony scent or guard defensiveness). Instead, we could run our comparative tests on empty hive bodies containing a scent that we’d trained foragers to be “sniffing” for.

So we scented sugar syrup with anise extract and dumped it into horizontal drawn combs placed twenty feet ahead and behind a group of four test hive bodies on bottom boards (Figure 4).

Fig. 4 Initially, after dumping the syrup on the comb, it took a while for the first scout to show up (presumably coming from one of the several dozen hives on the property), but it soon appeared to have recruited a mob. We repeated this baiting and training several times a day, day after day.

We ran our tests during our warm-to-hot September nectar dearth. The bees would abandon the comb once they’d taken all the syrup. But after the first training, investigators would quickly pick up the scent when we replenished the syrup, and call the gang back again. Meanwhile, there would be plenty of anise-trained foragers seeking out any other source of anise scent (Figure 5).

Fig. 5 I chose anise extract since there were no flowers with that scent in the neighborhood. Since all the foragers came from nearby hives, the scouts and investigators likely only performed round dances –– without specific direction –– so the recruits would be scouring the proximate neighborhood for the scent of anise, investigating any trace of the odor anywhere on the property.

Once trained to the scent, we could place trays of scented cotton (without any syrup) as attractants to the hives (Figure 6). We intentionally did not provide a sugar reward, since we did not want a bee that made it to the scent to recruit other foragers to that particular location.

Fig. 6 In order to quantify the number of bees that entered a scented hive through the robbing screens, I spent days making different designs of entrance traps of black screen, to no avail –– we were amazed and frustrated by how reticent investigating bees were to attempt to enter a hive with any screen present.

We tried everything, including placing tiny computer fans to blow the scent out through the entrances (Figure 7).

Fig. 7 We spent frustrating days in amazement. Plenty of investigating bees would fly back and forth in front of the entrances (exhibiting what many would call “robber flight”). But even without the presence of guard bees, danged if they would go in any sort of black-screened entrance tunnel (even though robbing bees, as many have found, will squeeze through any crack to get at unguarded honey).

So I wondered whether the investigating bees (potential “robbers”) had been trained through previous experience to recognize that the object in front of them was a beehive (identical to their own), and be exhibiting trepidation that there might be guards lurking in the entrance.

“Guilty” Flight Behavior

Any beekeeper soon recognizes the back and forth (zig-zag) flight of potential robbers in front of a hive, as described in 1954 by Free [[9]]:

Bees which are attempting to rob colonies of their stores of honey, fly to-and-fro in front of the hive entrance with a characteristic swaying motion as though watching for an opportunity to enter the hive unchallenged by its guards.

So is zig-Zag flight due to guilty intent, or is it “normal”?

After confirming how easy it was to train bees to scented sugar syrup, we assumed that it would be a simple matter to get scouts to enter a bee-free screen trap (so that we could count them to test the efficacy of robbing screens). Not so!

One thing that we noticed was that investigating scouts (or inspectors) orienting to the scent emanating from the entrances of our unguarded hive bodies exhibited similar “cautious” behavior, despite the fact that they had all flown from nearly identical-looking hives. As much as at the entrance, we’d see investigators flying around every crack or crevice in a hive body containing a scent lure. And despite having our tiny fans pushing a plume of scent out the entrance, the investigating bees would fly back-and-forth in front of the entrance, without even attempting to touch down on the landing board before flying off. It was frustrating for us to watch their hesitancy (view their exploratory hesitant flight at [[10]]).

I finally gave up on screened traps and found that if we gave them enough time, some of the investigating bees would eventually walk through an open entrance (or a robbing screen opening) to the scent lure.

Much later, I read in Norm Gary’s article about robbing that:

It should be emphasized that these new foragers are directed to the odor of this newly discovered food source. As these recruits begin to search they discover the location of the food by perceiving the abundant honey odor coming from colony entrances. Experiments have shown that there is a rapid rate of air exchange within the hive, as regulated by fanning bees. This colony “exhaust” odor is highly attractive to recruits. At this time they are unfamiliar with the “host” colony as a foraging vessel; consequently, their approach flight is somewhat erratic, and their learning experience is not helped by frequent attacks on the intruders by guard bees at the colony entrances. Thus, during this searching behavior the sidewise flight pattern is induced.

Significant to this discussion of robbing is the fact that the initial searching and orientation behavior near [new types of] flowers could be described as “hesitant,” or “unsure,” although not as “guilty” or “nervous.” After a brief learning experience, which may occur quickly if the problem [of obtaining nectar] is simple, experienced foragers become “sure.” They at last approach the food source quickly and in a manner that seems to indicate with the flower structure and nectar location.”

Aha! –– thanks Norm, maybe that back-and-forth flight was not due to guilt or fear of guard bees, but rather simply due to unfamiliarity with the new odor source. But how could I confirm this? Maybe I could test it by presenting the bees the scent on a natural-looking, but unfamiliar flower.

A Simple Experiment

We purchased some realistic-looking artificial flowers in yellow and purple, and set them out to observe the behavior of investigating bees (Figure 8).

Fig. 8 Despite appearing surprisingly realistic, foragers paid no attention to the artificial flowers until we placed a drop of the anise scent to the center of the corolla. Immediately plenty of (scent-trained) bees would be interested! But they didn’t just land where we had placed the drop, but first engaged in the same sort of back-and-forth investigative flight that they did in front of the empty scented hives, only eventually working their way to the center (they quickly abandoned the flowers when they found no sugar reward).

Practical application: We laid to rest the implication that the hesitant back and forth flight of bees investigating the scent emanating from a hive implied guilt or intent to commit robbery–– they do the same with a harmless-looking unfamiliar flower!

Back to our original question

I began our investigations into robbing screens to determine whether they helped to prevent the immigration of mites (by excluding drifting bees). Although our findings didn’t support a reduction in mite immigration [[11]], to our surprise, we found that robbing screens could clearly frustrate natal bees trying to enter their own hive to the point that they “give up” and enter other hives [[12]].

A robbing screen can clearly prevent foragers from figuring out how to enter their own hive. But that still leaves us with two questions:

Question #1: To what extent will scouts (potential honey thieves) from other hives, attracted to the scent emanating through a robbing screen, persevere before giving up and moving on?

Question #2: If a scout were to be successful at entering through the robbing screen of an unguarded (by bees) hive and return home with a sugary reward, would it be able to recruit additional “robbers” to that scented sugar source (by odor, since the round dance does not specify location, nor even more specifically, how to get past the danged obstructive robbing screen)?

You’ll find out next month!

Citations

[1] Quoted from The ABC and XYZ of Bee Culture, 41^st Edition.

[2] https://scientificbeekeeping.com/robbing-behavior-in-the-honey-bee-by-dr-norm-gary-1966/

[3] Vander Wall, S, et al (2003) Reciprocal pilferage and the evolution of food-hoarding behavior, Behavioral Ecology 14(5): 656–667 https://doi.org/10.1093/beheco/arg064

[4] Biesmeijer, J. C., & Seeley, T. D. (2005) The use of waggle dance information by honey bees throughout their foraging careers. Behavioral Ecology and Sociobiology 59: 133-142.

[5] von Frisch, K (1923) Über die ‚Sprache’ der Bienen. Eine tierpsychologische Untersuchung. In: Zoologische Jahrbücher (Physiologie) 40: 1–186.

[6] Moore, D, et al (2011). Diminishing returns: the influence of experience and environment on time-memory extinction in honey bee foragers. Journal of Comparative Physiology A, 197, 641-651.

[7] Wagner, A, et al (2013) Persistence, reticence and the management of multiple time memories by forager honey bees. Journal of Experimental Biology, 216(7): 1131-1141.

[8] Read about my observations at my screened exhibit https://scientificbeekeeping.com/a-survey-on-robbing-at-collapse/

[9] Free JB (1954) The behaviour of robber honeybees. Behaviour 7(2/3): 233-40.

[10] https://www.youtube.com/shorts/eLsXk2AZChg

[11] See parts 1-4 of this series.

[12] Can Robbing Screens Reduce MiteImmigration? Part 5. ABJ November 2024

Category: Varroa IPM Strategies, Varroa Management