Author: Heather Broccard-Bell, Ph.D., Honey Bee Health Researcher

In 1974, the American philosopher Thomas Nagel published an essay called, “What is it Like to Be a Bat?” [1]. In it, he argued that we can never really know because everything about how we perceive the world is coloured by the specific way in which our sensory systems operate. Even if we try to imagine what it might be like to be a bat, we unconsciously and unavoidably do so from our own biased perspective as a human, with human-type senses. For example, many of us think in words and/or pictures, neither of which a bat can do, even if it wanted to. Nagel argued that one can only truly understand what it is like to be a bat if one is actually a bat—and the same goes for knowing what it’s like to be a honey bee, or any other kind of non-human creature. In effect, Nagel’s essay really just expanded on the old saying, “you never truly know what it’s like for someone until you walk a mile in their shoes.”

Why would we want to know what it’s like to be another creature anyway? We encounter bee behaviours all the time that seem mysterious. Knowing why bees do the things that they do would certainly be helpful, and this starts with understanding what the world is like from their perspective.

So, if we can’t know exactly what it’s like to be a bee, what can we know? Fortunately, a lot of scientific research has been devoted to understanding honey bee sensory systems, giving us some pretty decent knowledge on the topic. I have been studying honey bees for the past seven years, but my formal training is actually in neuroscience. In this post, I am going to put my education to work to review what we know about how bees experience the world and how it is both similar to, and often different from, our own experiences. Recognizing these differences will, I hope, go some distance toward allowing you to better understand the behaviour of your honey bees from their perspective.

In part one of this series, we’re going to look at the honey bee’s unique visual capabilities and how these help in navigation, foraging, and more.

They Say Seeing is Bee-lieving…

When we experience the world, we don’t really experience everything that is out there. For example, we are surrounded by all kinds of naturally-occurring wavelengths of radiation [a]—from X-rays to microwaves and radio waves [b]—but visible light is the only kind we pick up with the types of receptors we have in our eyes. While visible light is all we see, this doesn’t mean the other types of radiation do not exist, nor that they cannot be detected by other kinds of organisms.

In humans, vision happens when particles of light (photons) interact with the sensory receptors, called photoreceptors, located on the rear inner surface of our eyes. When a photon activates one of these photoreceptors, a signal is sent to our brain. We have several types of photoreceptors, and each is sensitive to specific wavelengths and/or intensities of light. Amazingly, our brain adds up all the signals received from every photoreceptor in our eyes and integrates those into the images we see!

Although most creatures make use of light, many have photoreceptors that are not attuned to the specific range of light that humans see—and many are able to see parts of the electromagnetic spectrum that we cannot. Ultraviolet (UV) light, which has a shorter wavelength than what humans can detect, is now known to play an important role in the lives of many organisms. Using special photographic techniques, scientists have discovered that a whole array of different organisms are coloured with UV patterns that are invisible to humans. Chief among the organisms that use UV patterns are plants, whose UV patterning directs bees and other pollinators to the appropriate areas on flowers [2]. Honey bees are able to see UV light, and thus the patterns on flowers, but they are not able to see red light [3]. When I was doing research with observation colonies, I sometimes exploited this fact by viewing my bees under red lights in an attempt to disturb the bees as little as possible; however, like us, bees use multiple senses to take in what is happening around them, so even though they might not have been able to see me, it doesn’t necessarily mean they didn’t know I was there.

See Figure 1: Scientists are able to visualize UV floral patterns using false colour photography. On the left is a “visible light” image of a Yellow Day Lily (Hemerocallis lilioasphodelus), and on the right is the same flower showing the UV part of the spectrum. Note that in the UV range, the flower has clear dark markings around the centre that are not visible to us. These markings are thought to act as a guide for pollinators [2].

Image credit: Dave Kennard, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons.

Navigation Using Light

Another quality of light that bees pay attention to that we hardly notice is polarization. In the natural world, light is often unpolarized, meaning that it travels in many directions at once. To minimize reflection and enhance vision, especially outdoors, humans have invented camera filters and polarized sunglasses to filter out all the light except that travelling in one specific direction. When the light hitting our eyes comes from only one direction, we say that it is polarized (polarity = direction).

Interestingly, sunlight is polarized as it is filtered through Earth’s atmosphere. The specific direction of the polarization depends on the sun’s position in the sky, and how far away from the sun we measure polarity. We humans cannot readily distinguish between polarized and unpolarized light, and we certainly cannot tell the direction of polarity—but honey bees can! In a previous blog post about why honey bees are such great pollinators, I discussed the waggle dance and how bees use the position of the sun in the sky to navigate. What I didn’t tell you yet: the information that honey bees use is not the sun itself, but the polarization of its light. Navigation using polarized light rather than the sun is particularly useful because the sun isn’t always visible in the sky (e.g., when it’s cloudy); however, even when the sun is obscured, polarized light is still visible [5].

But How Do We Know?

The astute among you must be wondering exactly how we know what bees see. As we learned from Thomas Nagel and his bats, we can never really know to absolute certainty. I can’t even be 100% certain that I understand what you see, and you can tell me in words—never mind what a bee sees! Although we can’t be exact, scientists use a combination of different approaches to work at understanding a bee’s perspective. The best way to get the best information is to look at a lot of different sources [c]. If there is agreement across those different sources, you can be more confident that your information is accurate. Scientists use a similar technique to try to answer research questions using more than one type of experiment.

For example, we know that honey bees can detect UV light by understanding the basic neurobiology of the types of receptors they have in their eyes. Experiments show that these receptors undergo physical changes when they interact with UV light [6]. However, knowing that there is a physical change in a receptor is not enough to say that bees actually use this information. To determine that, scientists use behavioural experiments, such as testing if honey bees are able to distinguish between patterns that contain UV elements and those that do not [7].

For instance, when presented with feeders that have higher or lower concentrations of sugar, bees typically choose the higher concentration, provided they can tell the difference between the feeders (e.g., if they are in different locations, or are different shapes or colours). So, if we observe bees visiting a feeder with UV markings that has a high concentration sugar solution more often than a feeder without UV marking that has a low concentration solution—and provided that everything else about the feeders is exactly the same—then we infer that the bees are able to use the UV marks to tell the difference between the feeders [d.]. In an upcoming post, I will be talking in-depth about the limits of honey bee cognition, including learning and memory.

The Eyes Have It

The last topic I want to touch on with respect to vision is probably the most obvious: honey bees do not have the same type of eyes as humans. In fact, they don’t even have the same number of eyes! If you’ve ever looked very closely at a honey bee’s face, you might have noticed that there are three dots on the top of her head. These are called ocelli (singular: ocellus) and are a type of “simple eye”. The internal shape of ocelli means they probably do not form a clear image like our eyes [8], but scientists think they are both faster and more sensitive to light and motion than the bees’ larger compound eyes [9]. Potentially even cooler: it seems that ocelli are the eyes primarily responsible for the detection of polarized light that I talked about earlier [10]. So, it seems likely that ocelli have at least two purposes: quickly detecting fast-moving objects, and navigation.

See Figure 2: Three dots visible on the top of a bee’s head are “simple eyes” known as ocelli that allow bees to quickly detect light and motion. Photo credit: H. Broccard-Bell.

But what about those big compound eyes? Human eyes each contain a lens whose shape can be changed using muscles, which allows us to focus on objects that are both near and far from us. Each of our eyes has only one such lens, and each eye contains the full range of receptor types for detecting different intensities and colours of light. In contrast, honey bees have a whole bunch of lenses per eye—up to 10,000 in drones [11], but each lens is fixed, meaning it can’t be focused with muscles. Each lens is part of a separate tube-shaped organ called an ommatidium (plural: ommatidia), and it is the lenses at the ends of these tubes that we see on the surface of a bee’s compound eye.

In honey bees, there are distinct classes of ommatidia, and each class has a different complement of receptor types [12]. Each ommatidium is capable of capturing its own image, and each image captured is slightly different image from that captured by every other ommatidium in the compound eye, due to having different receptors and being in a slightly different location on the eye’s surface. Like human brains, honey bee brains also need to combine the information coming from the eyes to get a useful picture of the world. Compound eyes occur in a large number of animal species, ranging from insects to crustaceans (i.e., shrimp and crabs) and are clearly very useful; however, they do come with drawbacks. The main one is that, since ommatidia have fixed lenses, honey bees need to move their bodies closer to and further away from objects to be able to focus images.

Finally, you have possibly noticed that, quite unlike ourselves, honey bees have eye hair. No, I don’t mean eyebrows or eyelashes. I mean that honey bees literally have hair growing out of their eyes! Do these eye-hairs contribute to vision? Yes, albeit indirectly.

One of the honey bee’s many activities is to collect pollen. Pollen grains have a slight negative charge, and this causes them to be attracted to bees, which become positively charged during flight. The purpose of the eye-hairs seems to be to prevent pollen from building up on the surface of the eyes, obscuring vision [13]. Collecting pollen on hairs instead of eye surfaces also makes sense because bees already have special adaptations on their forelegs that allow them to easily comb pollen out of their hair.

See Figure 3: My, what hairy eyes you have, my dear! Photo credit: H. Broccard-Bell

Beauty is in the Eye of the Beholder

Like us, honey bees rely quite a lot on vision to navigate through their world—but as we have seen, the way they do this is rather different from humans. I am sure this leads some of you to wonder about the other familiar senses. Do honey bees have them? And if so, are they as peculiar as honey bee vision?

Good news: they do and yes, they are just as interesting!

In part two, I will dive into the honey bee’s other senses and how they are used. Follow along as we share more about the unique world of the honey bee!

FOOTNOTES

[a] We are constantly bombarded by naturally-occurring, and human-generated radiation of all sorts. As with many other things, though, the dose makes the poison, and the amount of harmful radiation to which we are normally exposed is largely negligible. One obvious exception is solar radiation. In particular, exposure to UVB (a sub-type of UV light) is linked to the development of skin cancer: https://www.epa.gov/radiation/radiation-sources-and-doses

[b] No, contrary to what your “alternative” uncle would have you believe, none of these are in fact human inventions. Microwaves, X-rays, and radio waves are all quite abundant in nature, and are produced by a large range of naturally-occurring processes: https://nuclearsafety.gc.ca/eng/resources/fact-sheets/natural-background-radiation.cfm

[c] A huge caveat to keep in mind is that not all sources of information (just like not all experiments) are created equal. When it comes to sorting out good from bad information, your “alternative” uncle’s blog post should almost certainly not have the same influence on your decisions as a scientific paper published by an expert.

[d.] Now I know that some of you will be wondering whether or not they are just picking the higher concentration feeder because it is has a higher level of sugar, but as I will discuss in the section on taste, when using pure, newly prepared lab-grade sucrose, bees cannot smell the sugar in the solution.

References

[1] Nagel, T. (1974). What is it like to be a bat. Readings in Philosophy of Psychology, 1, 159-168.

[2] Lunau, K., Scaccabarozzi, D., Willing, L., & Dixon, K. (2021). A bee’s eye view of remarkable floral colour patterns in the Southwest Australian biodiversity hotspot revealed by false colour photography. Annals of Botany. Doi: https://doi.org/10.1093/aob/mcab088

[3] Avarguès-Weber, A., Mota, T., & Giurfa, M. (2012). New vistas on honey bee vision. Apidologie, 43(3), 244-268.

[4] Kraft, P., Evangelista, C., Dacke, M., Labhart, T., & Srinivasan, M. V. (2011). Honeybee navigation: Following routes using polarized-light cues. Philosophical Transactions of the Royal Society B: Biological Sciences, 366(1565), 703-708.

[5] Evangelista, C., Kraft, P., Dacke, M., Labhart, T., & Srinivasan, M. V. (2014). Honeybee navigation: Critically examining the role of the polarization compass. Philosophical Transactions of the Royal Society B: Biological Sciences, 369(1636), 20130037.

[6] Menzel, R. (1975). Electrophysiological evidence for different colour receptors in one ommatidium of the bee eye. Zeitschrift für Naturforschung C, 30(9-10), 692-694.

[7] Jones, C. E., Scannell, C. L., Kramer, K. J., & Sawyer, W. E. (1986). Honeybee constancy to ultraviolet floral reflectance. Journal of Apicultural Research, 25(4), 220-226.

[8] Hung, Y. S., & Ibbotson, M. R. (2014). Ocellar structure and neural innervation in the honeybee. Frontiers in Neuroanatomy, 8, 6.

[9] Hung, Y. S., van Kleef, J. P., Stange, G., & Ibbotson, M. R. (2013). Spectral inputs and ocellar contributions to a pitch-sensitive descending neuron in the honeybee. Journal of Neurophysiology, 109(4), 1202-1213.

[10] Ogawa, Y., Ribi, W., Zeil, J., & Hemmi, J. M. (2017). Regional differences in the preferred e-vector orientation of honeybee ocellar photoreceptors. Journal of Experimental Biology, 220(9), 1701-1708.

[11] Streinzer, M., Brockmann, A., Nagaraja, N., & Spaethe, J. (2013). Sex and caste-specific variation in compound eye morphology of five honeybee species. PLoS One, 8(2), e57702.

[12] Wakakuwa, M., Kurasawa, M., Giurfa, M., & Arikawa, K. (2005). Spectral heterogeneity of honeybee ommatidia. Naturwissenschaften, 92(10), 464-467.

[13] Amador, G. J., Matherne, M., Waller, D. A., Mathews, M., Gorb, S. N., & Hu, D. L. (2017). Honey bee hairs and pollenkitt are essential for pollen capture and removal. Bioinspiration & Biomimetics, 12(2), 026015.