Honey bees (Apis species) appear to be unique, in that they are the only social bees which can recruit other members of their hive to come and join them in foraging at a specific resource site, say a patch of flowers. Individual foragers are able to communicate the location, odour, and presence of high-quality food, or potential nest sites, to their nestmates. As explained below, they can transfer information on the direction of the nectar-bearing flowers and the distance the bees must fly to get to the advertised nectar source, using a remarkable behaviour, called the waggle dance. In this blog, we look at the European honey bee (Apis mellifera), where these dances are performed within the hive, after foraging and selecting nest sites.

In her wonderful book, The Bees, author Laline Paull describes how a ‘nectar-scented forager’ communicated with the other bees:

“she began to dance. Slow and clear she stamped out a simple phrase, over and over until the bees understood it and the rhythm caught.”

“Go South! sang the bee’s steps. For this long!”

In other words, the forager was conveying information about the direction and distance of a newly discovered nectar source – such as a patch of flowers – to her fellow nest mates. Although this book (The Bees) is a novel, it contains elements of bee behaviour that we know to be true, thanks to the work of generations of bee biologists (apiologists) who have carefully teased apart this extrodinary insect behaviour.

The first person to discover this behaviour was an Austrian entomologist called Karl von Frisch. Frisch was carrying out experiments on the visual and olfactory abilities of honey bees in Germany (1917), using feeding dishes containing sugar water, when he noticed that when he replenished the dishes, a large number of bees quickly appeared. He realised, or at least hypothesised, that the bees must somehow have communicated to their hive mates that the sugary food was again available (Munz, 2016). In other words they said ‘come and get it’ to the other bees! It wasn’t until a few years later, in 1919, when he had obtained a glass-plated observation hive and could view the action inside the beehive, that Frisch discovered that the bees performed a kind of “dance, he called it a ‘recruitment dance’, which brings her nearest surroundings into noticeable excitement” (von Frisch, 1973).

Von Frisch first described what came to be known as the round dance (see below), in 1919:

“She [the honeybee] scurries with great speed in a circle, but at the same time often pivots by 180 degrees, so that the direction constantly changes“.

In the round dance (above), the bee walks in a circle, turns around, then walks around the same circle, but in the opposite direction. The round dance indicates the presence of a desirable food source close to the hive, but provides no information about its direction. The more elaborate waggle dance (see below) indicates the presence of a food source >100 m from the hive, and provides information about both its distance, and direction, from the hive. According to Tania Munz, in her 2016 book, The Dancing Bees, Frisch initially believed that the circle and waggle dances served to communicate nectar and pollen sources, respectively, but later revised this interpretation and argued that the different dances corresponded to nearby and far-away sources.

Frisch described the round and waggle dances as being  separate ‘words’ in the language of the bees (von Frisch, 1967), but they are now thought of as being two ends of a continuum. In other words, honeybees have just one adjustable recruitment signal: the waggle dance. The regularity of the pattern of alternating left and right turns made by the bee, ‘decreases in a nonlinear fashion as the distance between the hive and the food source decreases’ (Gardner et al., 2008). One second of waggle dancing approximates a kilometre of flight.

Let’s take a step back and consider the beehive, which typically contains about 10,000 individual bees, but can increase to as many as 50,000 in the height of the summer. During this period of peak breeding, the proportion of foragers can be as high as 30% of the colony. This foraging work force is further divided into groups of bees specializing in collecting different resources: e.g. water, nectar, honeydew, pollen, or propolis (plant resin). Remarkably, each of these foragers can assess the resource quality of, say a patch of flowers, by evaluating, not only the volume and concentration of nectar present, but also how far it is from the hive, and even the likelihood of predation! N.B. the non-foraging hive (or house) bees stay at home to rear the brood and maintain the nest, but the get to go foraging later on in their lives!

When a successful forager returns to the hive after discovering a rich food source she is greeted by other worker bees who induce her to regurgitate her nectar load to them. If they are sufficiently impressed by the quality of the nectar, the forager starts waggle dancing for them on the vertical sheet of comb, and she is eagerly followed by a small band of bees. Foragers that are kept waiting and have difficulty finding a food-storing, receiving bee to take on their nectar, sometimes carry out a tremble dance, or Zittertanz in German (Seeley, 1992). The tremble dancing bees move across the comb making ‘irregular running, shaking, vibrating, and trembling motions’ while rotating about their body axis (Lam et al., 2017). The function of the tremble dance seems to be to recruit more bees within the hive to become food unloaders, but may also indicate crowding of nectar foragers at the food source! In effect, these trembling bees are putting the brakes on nectar gathering, and signaling a need to increase the rate at which the hive processes the incoming nectar (Kirchner, 1993).

During a typical waggle dance, the bee moves forward on the surface of the honey combs while vigorously shaking her body from side to side: the waggle run phase of the dance (see above). This all takes place at specific sites on the vertical honeycomb surfaces within the dark hive, so exactly how the information contained in the dance sequence performed in the darkness of the nest is transferred to the other bees, is a bit of a mystery. Nevertheless, it seems that the dance can be followed by the nestmates in the dark, because her wing vibrations produce airborne acoustic signals and air flows, behind her. So, the bees following the dancing forager play close attention to rhythmic sounds and vibrations that the dancer produces, and somehow they filter out all the other noises made by the thousands of other bees in hive!

At the end of the waggle phase, the bee turns to the left or right, circling back to start the waggle phase again. The dancing bee alternates the direction in which she turns, after the waggle phase, thereby tracing out a figure-of-8 pattern (see below). Directional information is communicated by the angle of the waggle phase relative to the vertical in the beehive, which corresponds to the angle of the resource patch from the sun’s azimuth. Distance information is conveyed by the duration of the waggle phase, and the attentive followers, facing the dancer from the side, touch it simultaneously with both antennae, and appear to use this tactile stimulation to gague the direction and duration of the dance (Gil & De Marco, 2010).

Returning foragers only dance if the recently visited food source is ‘profitable’: that is to say they are excited by it. The better the food source, the more waggle runs the forager performs: the livelier the dance. So the number of complete waggle dances a returning forager makes will vary according to resource quality (Seeley et al., 2000). I.e. inter-dance variation. There is also a degree of variation in the angle and duration of repeated dances from a given individual (i.e. intra-dance variation, or ‘noise’), so the follower bees (potential recruits) take an average of the runs, i.e. in order to derive a single values for both distance and direction (see Couvillon et al., 2012).

The follower bees, have to be able to ‘read’ the multisensory language of the dance. However, individuals differ in terms of how quickly they pick up the information provided by the dancer. Some recruits are able to find the resource after watching only a few waggle runs, say five or six, while other followers need to observe dozens of waggle runs in order to decode the information the dancer is trying to communicate to them. Researchers found that some bees never managed to find the food source, despite ‘watching’ (it’s in the dark!) more than 50 waggle runs and making a number of trips to search for it. It’s hard not to think, that like humans, and most animals I suppose, some individuals are cleverer than others! Or maybe, some bees need more arousal and stimulation than other, and some bees might just be bad learners! (Grüter & Farina, 2009).

However, despite having evolved this wonderful means of communication, many bees simply ignore the information that the dances contain. This seems to be because many of the followers rely on their own memories of particular locations, which they have learnt over previous days or weeks, when out and about visiting food patches. Scientists call this, ‘private information’, as opposed to the ‘social information’ which foragers have shared with their followers within the hive. In one study, 93% of foragers relied on their own private information about the location of a good food source, rather than investigating the new resource described via the dance language (Grüter et al., 2008). Also, the value of discovering a new, rich food source depends on how common such floral food sources are in the environment around the hive, and how they are distributed, i.e. whether they are homogeneous or clumped (Dornhaus & Chittka, 2004).

There is still much to discover about honey bee communication and this blog has only dipped a big toe in the subject! Exactly how honeybees are able to translate the spatial position of a resource they have found in the real world – after flying there and back for a certain time and direction – into movements and motions (e.g. buzzing their wings) back in the hive, i.e. the dance language, is something scientists will continue to investigate for some time, I think.

Karl von Frisch famously described the honey bees and their dance language as a “magic well” of scientific discovery (Dyer, 2002), and the well continues to yield its bounty to those willing to spend the time studing these amazing insects.

Links

https://www.sciencedirect.com/topics/neuroscience/waggle-dance

https://theconversation.com/amp/unlocking-secrets-of-the-honeybee-dance-language-bees-learn-and-culturally-transmit-their-communication-skills-200896

References

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