How does the world look like through the eyes of bees? And can bees hear? In this issue of ApiGuide, we focus on the senses of bees. Even though they are really small, bees have an excellent awareness of their environment. They can even feel things that are hidden from us. For example, the bees feel the Earth’s magnetic field, can see in UV colour and the polarisation pattern of the sky.
The multi-faceted eyes of honeybees consist of up to 8000 individual eyes, the so-called «ommatidia». Although the bees have a large field of vision, they are short-sighted and can only see sharply in the centimeter range. A human can distinguish two points at a distance of 18 m as separated, while a bee can do this at only 30 cm. In contrast, bees have a much better temporal resolution. Bees are able to resolve up to 200 images per second, while humans can only perceive 20 images per second. This high resolution gives bees a quick reaction time and is also important for the estimation of distances (see below under orientation).
Colour vision is especially important when looking for potential food sources. In contrast to humans, bees do not see red, but they can perceive colours in the ultraviolet range, which we are not able to detect. For example, rapeseed blossoms have a colourful pattern for bees – the so-called nectar guides in UV colour (Figure 1). These nectar guides are arranged concentrically around the crown tube and show the bees the way to the nectar. It has been shown that bees find nectar faster on flowers with nectar guides. By nature, bees prefer flowers with such patterns compared to single-coloured flowers.
The sense of smell of the bees is located in their antennae. Compared to other insects, bees smell very good and have 170 different olfactory receptors. Odors plays an important role in their lives – both in communication within the colony and in the search for food. Various scents, so-called pheromones, regulate the coordination of the different tasks in the hive. The best known pheromones are the queen pheromone, which indicates the presence of the queen, and the alarm pheromone, which is released by the workers in danger and triggers aggressive behavior. The foraging bees, on the other hand, use the scent of flowers to locate sources of nectar and pollen. These so-called olfactory flower signals are already perceptible at long distances, whereas the visual signals only play a role at short distances. During their flower visits, the foragers also leave scent markings; these serve as information for other forager bees and save them from visiting already «empty» flowers.
The taste receptors of the bees lie on their antennas, mouth parts and the feet of their forelegs. They serve the perceiving of substances dissolved in liquids. The sense of taste plays an important role in the choice of food sources and in the recognition of hive companions. The receptors consist of small hairs which react to sugars, salts and amino acids. So far, 10 receptors have been identified; in contrast to humans, bees cannot perceive bitter substances.
Bees hear with the so-called «Johnston’s Organ», which is located in the antennas. It is used to perceive sounds from the nearby environment like air vibrations. Such noises play an important role in the communication within the colony, like with the waggle dance. Bees are able to move by flapping their wings and moving their thorax muscles.
Bees can perceive the earth’s magnetic field and use it for orientation during foraging flights and for cell alignment during honeycomb construction. The perception is done through the iron particles located in the bees abdomen which align with the magnetic field.
Learning and Orientation
Position of the sun
Bees are little wise guys. Not only do they have excellent learning abilities, but they also have a good memory. Like humans, bees have short and long-term memory. During their first excursions from the hive, bees learn various landmarks such as trees and houses as well as the direction of the sun during the course of the day. By doing so, the bees know how the angle of the sun to stationary landmarks changes over the course of the day. Thanks to this inner map, they can later find their way back to the hive at any time. Unlike humans, bees can also perceive the polarization pattern of the sky, which is generated by solar radiation and depends on the position of the sun. This means that bees recognize the position of the sun even when the sun itself is not visible.
In order to navigate through their surroundings, bees need to be able to measure distances. They do this by registering the so-called «optical flow». In other words, they perceive the optical image flow that passes by them during the flight. This mechanism could be shown with an experiment, where bees had to fly through striped tunnels. With narrowband patterning, the bees had a higher image flow than with broadband patterning. According to this image flow, the bees then estimated the flown distances.
Learning also plays an important role in the search for food. If collecting bees find a plant species with a good supply of nectar or pollen, they can remember its flower shape, color, scent and even surface texture. By remembering this they can easily find other plants of the same species. Because the bees also have to learn how to get food quickly in the flowers, but only have limited memory, the collecting bees visit only one plant species for a while. This greatly increases collection efficiency. This specialization is called flower constancy and is also to the advantage of the plants, which are more frequently pollinated with pollen of the same specie and are therefore better pollinated.
The learning ability of the bees is so good that they can even remember faces and keep different people apart. This could be proven in an experiment in which the bees were presented with photographs of human faces in combination with sugar and salt solutions. The bees were able to remember which faces contained the sugar solutions and flew to them more often. So the bees know who is stealing their honey!
1 Leonard, A. S., Papaj, D. R. ‘X’ marks the spot: The possible benefits of nectar guides to bees and plants. Functional Ecology 25, 1293-1301 (2011)
2 Lehrer, M., Horridge, M. A., Zhang, S.W., Gadagkar, R. Shape vision in bees: innate preference for flower-like patterns. Philosophical Transactions: Biological Sciences 347, 123-137 (1995)
3 De Brito Sanchez, M. G. Taste perception in honey bees. Chemical Senses 36, 675-692 (2011)
4 Dreller, C., Kirchner, C. W. Hearing in honey bees: Localization of the auditory sense organ. Journal of Comparative Ecology 173, 275-279 (1993)
5 Lambient, V., Hayden, M.E., Reid, C., Griesm, G. Honey bees posess a polarity-sensitive magnetoreceptor. J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 293 (12), 1029-1036 (2017)
6 Barron, A., Srinivasan, M. V. Visual regulation of ground speed and headwind compensation in freely flying honey bees. The Journal of Experimental Biology 209, 978-984 (2006)
7 Dyer, A. G., Neumeyer, C., Chittka, L. Honey bee vision can discriminate between and recognise images of human faces. The Journal of Experimental Biology 208. 4709-4714