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Photo of David Roubik Bee Lines

What's the latest buzz in bee communication? Frontiers viewers found out from two who know: David Ward Roubik, resident bee expert at the Smithsonian Tropical Research Institute; and James Nieh, who studied stingless bees while completing his Ph.D. at Cornell University. Following the Frontiers special Expedition Panama: Bee Lines, David and James answered viewers' questions in an Ask the Scientists panel. Here are viewers' questions and their answers:

QCan you really tell what bees are saying just by the height and length of their buzzings sounds? How long did it take to piece this research together?

(Nieh): The bees produce sounds while unloading food and while dancing. When they are dancing, they produce sound pulses and the length of these pulses increases with the distance to the food source. Because I have data from several different years, I am fairly confident that I can tell how far away they are foraging from the length of these dance sounds. I do not have as much data on how the length of unloading pulses changes with the height of the food source, but I believe that I could roughly tell whether these bees were foraging on the ground or high in the canopy. In total, it has taken me 6 years to put this all together. Thanks for the question!

QMy dad has a book called "The Dancing Bees" by Karl von Frisch. That book says that the bees von Frisch studied tell other bees what direction the source of food is by the way they dance. On the TV show it said the bees you are studying communicate the distance and height of the food source by the buzzes they make. But it said you had not figured out yet how your bees communicate direction. The question is, do you think it could be in the little dance the bees do in the hive, and is the dance the bees in Panama do different from the dance von Frisch's bees do?

Good point and question. We see a lot of motions and hear a lot of sounds coming from the returning foragers, and all this greatly resembles the dancing know for Apis. What we can't seem to decipher is whether the constant turning clockwise and counterclockwise by returning Melipona is 'encoding' information of some sort about which way (compass direction) the resource target lies.

There is more, too. Our experiments did disrupt one important part of the hive environment -- the actual entrance to the nest, where there are a few bees guarding the entrance, and very close quarters in general. This area isn't really the dance floor or inside the hive, but neither is it outside the nest. Something important could be happening there which we have not so far taken account of. More experiments are on the drawing board right now, to see if we in fact do have a place where direction information is communicated, but neither in the main body of the hive nor outside somewhere in the forest on the way to the food.

QWhy doesn't this species of bees have stingers?

(Roubik): Stingers didn't work too well, or didn't work at all, for the stingless bees, somewhere in their evolutionary past -- so they 'lost' them. They were not worth the energy and material needed to maintain them, so that they were not helping and actually hurting the bees and their colonies. Natural selection worked to eliminate such useless structures, over some period of time. This process, in nature, is generally called 'atrophy'. Kind of like the front pair of gimpy legs on a T. Rex. They aren't used for much, so they kind of shrivel up. In the stingless bees, the stinger is really still there, it has just shriveled up to the point where it isn't visible to the naked eye.

From all indications, some of the early stingless bees were really very tiny creatures, about a quarter of an inch long. I've always suspected that their important predators could be thwarted by biting, and also by the bees exclusively nesting within very hard to get at, protected cavities -- like hollows in living trees. Honey bees use such tree hollows too, but many have a big hole leading into them, through which a predator could pass. The stingless bees, in contrast, are extremely careful about selecting the site where they build their nest. If a potential nest cavity has a fairly big hole leading to it, say, about the size of your fist, most will not use it. The few that will have very elaborate nest architecture, building thick, defensive walls from mud and stones mixed with resin, and have alarm pheromones and biting behavior. Our Panama bee, Melipona panamica, is just one such species.

QHave you had any breakthroughs in your research about bee communication since this show was filmed? Do you have any plans for new experiments?

(Roubik) You bet. Last month I spent in the canopy of Borneo, with another kind of social bee, called Apis koschevnikovi, or the "Borneo honey bee". This bee only lives in the incredibly tall, dense forests of Borneo, where trees reach 200 feet in height. Due to the constant efforts of my late friend, Dr. Tamiji Inoue of Kyoto University, Japan, we had the ideal setup in Borneo to test the behavior of the Borneo honey bee. We had three canopy towers, reaching 50 m (160 ft), and two hived colonies of the Borneo bees. With the aid of one or two field assistants, I ran 20 experiments training bees to a particular feeder and then putting out three feeders, at different heights, to see where the new recruits would arrive. They were four times more likely to go to the right feeder on their first try, no matter at which level it was placed.

We're getting there with these bees, but they were much harder to work with than the Melipona panamica back home. After opening their hive, the entire colony would abandon the nest on their next day. Clearly, we have to invent a much different strategy and set of techniques with which to work with these little creatures. And they are beautiful bees, too.

QHow far is the range over which the bees are able to communicate a foodsource or other information? How high in altitude do bees fly? How fast do they fly?

(Nieh): The Melipona seem to have a flight range limited to 1 to 2 kilometers. I have only been able to train them to an artificial food source that is 350 m away from the hive, and other researchers have trained them to a food source that is 800 m away. As yet, we do not have a clear understanding of their communication range; however, I would guess it would be between 800 m and perhaps 2 km. Bees often seem to fly above the rain forest canopy. In Panama, this is 40 m high. Their average flight speed is 5.6 meters/sec.

QHave you made any new discoveries about bee communication since this show was filmed? Is the research you are now doing in Germany adding to the knowledge you gained in Panama?

(Nieh): I have not been out in the field since the show was filmed, however there are several other important pieces to the story that could not be included.

(1) I have found that the bees deposit a scent beacon at the food source and that recruits are able to home in on this beacon from 12 m away (beyond12 m, the scent beacon does not seem to matter). The source of this scent is still a mystery, but it is not produced in the mandibular gland or in the fluid that they exude from their abdomen.

(2) I have carefully analyzed the spinning movements of bees inside the hive and found no relations between the direction of the spins, the order of the spins, the magnitude of the spins, or the speed of the spins and the direction of the food source inside the hive. So these spins do not appear to communicate direction.

(3) The bees do not always communicate the location of the food source. At times when they are extremely starved and when the food is very rich, they flood the area with recruits that randomly search for the food source. When you then give them poor food, they start to communicate the specific location again. I am currently working on a mathematical model that tries to explain this strange result.

It works like this. If you try to tell a friend how to get to the gas station, you can be very accurate, draw a map or tell him every corner to turn and each landmark or you can be extremely vague and say "walk around for a while." When you are very specific, you need to spend a lot of time explaining but your friend will not get lost. When you are very vague, you spend very little time explaining and your friend will probably become lost. Every second a bee spends communicating is a second that delays her from collecting food. Of course she also gets more help by communicating, but in special situations, it may be better for her to not communicate very much and to spend more time collecting food.

Right now in Germany I am learning how to use lasers and other equipment to measure the vibrations and sounds produced by bees. I believe that vibrations may be an important way for the bees to communicate and I hope to test this idea in the future with the techniques I am currently learning.

QHow do the bees learn the dances they do to tell the other bees where the food is?

Although bees may become better at using the information given in the dances with experience, they are born with the knowledge of how to understand the dance. Such knowledge is called "innate" because it does not need to be learned. Interestingly, humans are born with extremely little "innate" knowledge, unlike most of the animal world.

QIn the show it was mentioned that the bees sometimes leave droplets of liquid on leaves and such as they fly in search of food. Is the composition of this liquid known?

A chemical analysis of these droplets has been performed by scientists in the Netherlands on a difference species of Melipona, the stingless bee which I studied. These scientists have found that the droplets contain trace amounts of carbohydrates and amino acids.

QIn what other ways can bees communicate? Erica Sepulveda St. Anne School Houston, TX

There are several mechanisms by which bees can communicate, ranging from simple to extremely complex. Some bees indicate by their sounds and behavior inside the hive that food is available somewhere outside the hive. They do not specify the location. Other bees follow each other to the food source. Others deposit a scent trail. After finding a good food source, a forager will fly back to the hive, but along the way she will periodically land and rub her mandibles against a piece of grass or a leaf. By landing every few yards, she deposits a trail of droplets on the ground. However, we do not understand exactly how other flying bees may follow this trail. Another scent mechanism is to deposit pheromones (special scent chemicals produced by the body) at the food source. Other bees can then home in on this scent (but only when they are near the food source). The most complex is the honey bee dance language. Honey bee foragers measure the distance from the hive to the food and also the angle of the food relative to the angle of the sun. Because the honey comb is oriented vertically, they perform a special waggle dance that indicates the sun-food angle on the vertical hive surface. This communication mechanism uses sounds, vibrations, and motions inside the hive. Incredibly, the bees also have an internal clock that guides them in using a their sun compass to calculate angles. When they cannot see the sun on a cloudy day, they can use small patches of blue sky to tell where the sun is, because their eyes are sensitive to ultraviolet light, something that we cannot see. The sun produces special patterns of ultraviolet light in the sky that the bees can detect. When the sky is completely overcast and they cannot see any blue sky, they rely upon landmarks.

The himalayan honey bee, Apis dorsata, often collects food at night, and uses landmarks and the light from the moon and stars to help orient itself. However, it still measures the angle from the sun to the food source! How can it do this? Because it has a clock and a sun compass, it knows where the sun is on the other side of the world! If you observe the dances, you will see that it dances as if the sun were on the other side of the world.

QCan you please tell me where I can read more about your bee communication work? Is it published or available on the internet? Thank you.

I am afraid that it is not available on the internet, however, I can give you references for some publications:

Nieh and Roubik (1995) A stingless bee, Melipona panamica, indicates food location without using a scent trail. Behavioral Ecology and Sociobiology 37:63-70

This is a more technical journal that is difficult to find at most public libraries, but should be available at universities. Two other good papers are:

Lindauer M, Kerr WE (1960) Communication between the workers of stingless bees. Bee World 41:29-41, 65-71

Esch H, Esch I, Kerr WE (1965) Sound: an element common to communication of stingless bees and to dances of the honey bee. Science 149:320-321

The journal "Science" should be available in nearly all public libraries as well as at universities. "Bee World" is written mainly for bee keepers and bee enthusiasts, however it may be difficult to find. I have several manuscripts that have been submitted for publication, but this process will take at least 1 year. Thanks for your interest!

QUntil I saw this show I did not know there were stingless bees. What exactly are "stingless" bees? How do they defend themselves? How do they compare with "honeybees" and the so-called "killerbees"?

A very interesting question. Although stingless bees can bite and some also produce a painful chemical in their saliva, most of these bites are painless for large animals such as humans. So there is no logical reason to be afraid of them. However, stingless bees go for the hair and other dark areas of the body. Here they attach with their jaws and produce ferocious buzzing noises. If you have ever been stung by a wasp or a honeybee, it is easy to panic. Thus their "bark" is worse than their bite, but the "bark" is enough!

The sting of an Africanized honey bee is not more painful than the sting of a regular honeybee. However, the alarm response is much greater for Africanized honey bees and they will chase you farther. Thus you are more likely to receive many stings.

In the forest, their main predators are animals such as the taira, a wolverine-like animal, with strong, massive claws that can rip apart some bee nests. These nests are their main defense. They are made of mud, sticky resin, and wax and can be as hard as concrete. It is often difficult even with a chainsaw to cut through an old nest! Nests are made in tree cavities often high above the ground and, if there is space in the cavity, the bees make their nest stronger and stronger each year by adding more building material. A Melipona nest is similar to a human fortress. There is only one small entrance through which only one bee can pass at a time. Immediately inside the nest, several balls of resin at kept ready and the bees can roll these balls to block the nest entrance against enemies such as ants and other bees.

QWhy did you use colors on some bees? What kind of adhesive do you use for the numbers? How long do the tags stay on the bees? What happens if they fall off? Tim Gregor St. Anne School Houston, TX

It is easier to paint bees than to glue the labeled tags on them, so I prefer to use the colors. The paint is made of powdered paint pigment with shellac (a substance that is produced by the lac insect) and sticks quite well to insect cuticle. The tags are made of plastic and are glued with balsam resin (collected from balsam pine trees). Both methods of marking are highly durable and are used by honey bee keepers to mark queen bees who can live for many years. However worker stingless bees only live for a few weeks, so the tags rarely come off. If the paint or the tag has been poorly applied, one usually sees a bald spot on the bee where the paint or the glue has pulled off the hairs. Also, some traces of paint and resin usually remain.

QAn article published in 1969 by Drs. New and New in the Journal of Experimental Biology reports that the bees they studied changed the direction of their dance from clockwise to counterclockwise at zenith passage (when the sun is directly overhead). These researchers reported that the bees could tell zenith passage even on overcast days. Did you notice if the bees you worked with in Panama did this too? In one of your responses you stated that you could tell that certain bees were orientating their dance with the sun at night, even though it was on the other side of the earth, what exactly did you mean by that?

I did not notice any switch from clockwise to counterclockwise during noon. I found that bees were equally likely to clockwise or counterclockwise turns at any point during their dance and in random order. Regarding the dancing of the giant Asian honey bee, Apis dorsata, I have not observed the dances personally myself, but I have read that the bees continue to use the sun as a reference even though it is on the other side of the earth. A honey bee makes her waggle run at an angle to the vertical. If the food is in the same direction as the sun's azimuth from the hive (pretend you are drawing a line from the hive to the sun and then drop this line all the way to the ground). If the food source lies along this line, then the honey bee will make her waggle run vertically, moving upwards in the hive. If the food source is in the opposite direction along this sun-azimuth line, the honey bee will again dance vertically, but now facing directly DOWN. Because the sun moves during the day, the angle at which she dances will change over time to reflect the relative position of the sun's azimuth to the food source. Because the earth is rotating, the azimuth changes and at night the azimuth can still be calculated even though the sun is on the other side of the earth (imagine drawing a line through the earth to the sun now on the opposite side of the earth). If you know how the azimuth changes and if you have a clock, you can easily calculate where the sun should be, even though you cannot see it. This is exactly what bees are able to do. I suggest looking at an excellent book by Karl von Frisch called The Dance Language and Orientation of Bees (1967) Harvard University Press.

QHow many different types of bees are there? Do you think there are still new species to be discovered?

(Neih): Good question (and a tough one). The bees form a very large and diverse group including honey bees, bumble bee, stingless bees, sweat bees, etc. There are currently several hundred species of stingless bees alone. I'm afraid that I can't give a good figure for all bees, but there are certainly more species to be discovered.

QHow did you come up with the experiments that help you figure out how bees communicate?

(Neih): The basic experiments followed examples created by Karl von Frisch and his student Martin Lindauer (von Frisch discovered the dance language of the honey bees). Most of the experiments also occurred to me after observing the bees in various situations and wondering how they would behave if these situations were taken to extremes. I think the best way to design experiments is to first intensively watch your organism, really try to think what is important in their world and what specific problems they might face, then think of simple ways in which to test their abilities to solve these problems.


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