Honeybee Communication

The domestic honeybee, Apis mellifera, is a colonial insect living in hives containing:

one queen - a fertile female
a few drones (males)
thousands of workers (infertile females)

The workers are responsible for:

keeping the hive clean
building the wax combs of the hive
tending the young
foraging for food: nectar and pollen

When food is discovered by "scout" workers, they return to the hive. Shortly after their return, many foragers leave the hive and fly directly to the food. The remarkable thing about this is that the foragers do not follow the scouts back (the scouts may remain in the hive for hours). So the scout bees have communicated to the foragers the necessary information for them to find the food on their own. It turns out that the scouts can convey to the foragers information about:

the odor of the food
its direction from the hive
its distance from the hive

Distance

When food is within 50-75 meters of the hive, the scouts dance the "round dance" on the surface of the comb (left).

But when the food is farther than 75 meters from the hive, the scouts dance the "waggle dance" (right). The waggle dance has two components:

a straight run - the direction of which conveys information about the direction of the food
the speed at which the dance is repeated which indicates how far away the food is.

The graph shows the relationship between the speed of the dance and the distance to the food. It is based on data collected by the German ethologist Karl von Frisch. It was he who discovered much of what we know today about honeybee communication (and was honored with a Nobel Prize in 1973).

How do the bees calculate distance? von Frisch thought they measured the distance by assessing the amount of energy it took to get there. But the mechanism turns out to be quite different. The bees measure distance by the motion of images received by their eyes as they fly. Honeybees, like all insects, have compound eyes. These give little information about depth but are very sensitive to "flicker effect". It has long been known to bee keepers that honeybees respond better to flowers

moving in the breeze
with complex petals

The importance of flicker effect can be demonstrated by training honeybees to visit food placed on cards with patterns. For example, the bees can distinguish any figure in the top row from any figure in the bottom row more easily than they can distinguish between any of the figures in either row.

The Evidence

1. Working at the University of Notre Dame (Indiana), Esch and Burns found that when the hive and food were placed on top of tall (50 m) buildings, the speed of the waggle dance indicated a distance only half of the distance indicated by bees travelling the same distance (230 m) at ground level. Features of the scenery pass the retina faster when near than when far (compare the changes in your view from an airliner at 35,000 feet and as it approaches the runway).

2. Working at the Australian National University, Srinivasan and his colleagues built tunnels decorating the interior walls with patterns to create flicker.

Tests of Searching Behavior

In all these experiments, the bees were first fed in the middle of the tunnel of standard diameter. Then the food was removed.

Using the same tunnel, foragers came to same spot in the tunnel.
Using a narrower tunnel, foragers began searching for food near its entrance. Forced to fly closer to the vertical stripes, the images moved by faster.
Using a tunnel with a larger diameter, foragers searched for food at its far end. Flying farther from the stripes, the images moved by more slowly.

Tests of Dancing Behavior

All tunnels were 6 meters long and located 35 meters from the hive - well within the distance (50-75 m) that normally elicits the round dance.

Bees were fed at the entrance. Back at the hive, they danced the round dance as you would expect.
Bees fed at end of tunnel. Back at the hive, they danced the waggle dance. Even though the total distance from the hive (41 m) was still well within the "round" range, the complexity of the scenery passed in the last 6 m, elicited the waggle dance.
Bees fed at end of tunnel decorated with horizontal stripes. These created no flicker as the bees flew, and on their return to the hive they danced the round dance.

Direction

By itself, the knowledge that food is 6 kilometers (3.7 miles) away is not very useful. But von Frisch also noted that the direction of the straight portion of the waggle dance varied with the direction of the food source from the hive and the time of day.

At any one time, the direction changes with the location of the food.
With a fixed source of food, the direction changes by the same angle as the sun during its passage through the sky.

But

The sun is not visible within the hive.
The scouts dance on the vertical surface of the combs.

How, then, do they translate flight angles in the darkened hive? The figure shows how.

Relationship between the angle of the dance on the vertical comb and the bearing of the sun with respect to the location of food.
When the food and sun are in the same direction, the straight portion of the waggle dance is directed upward.
When the food is at some angle to the right (blue) or left (red) of the sun, the bee orients the straight portion of her dance at the same angle to the right or left of the vertical.

Other features: Time Sense When scouts remain in the hive for a long period, they shift the direction of the straight portion of the waggle dance as the day wears on (and the direction of the sun shifts). But they cannot see the sun in the darkened hive. Evidently, they are "aware" of the passing time and make the necessary corrections.

The time sense of honeybees has long been known to people who have sweet snacks in their garden at a set time every day. Within minutes of the regular time, foraging bees arrive for their share of the jam.

The speed of the bee's clock seems to be related to its metabolic rate. If normally punctual bees are

chilled (to lower their metabolic rate) or
exposed to an anesthetizing concentration of carbon dioxide

they arrive late to the picnic table.

Polarized light

von Frisch also discovered that scouts (and foragers) don't actually have to see the sun to navigate. As long as they can see a small patch of clear blue sky, they get along fine. This is because sky light is partially polarized, and the plane of polarization in any part of the sky is determined by the location of the sun. Try it by rotating a pair of polaroid® sun glasses!

Swarming

Before a new queen emerges, the old queen leaves the hive, taking many of the workers with her. The swarm usually settles somewhere, e.g., on a tree branch, while scouts go searching for a new home.

Each scout that finds a promising site, returns to the swarm and dances on it just as though she had found food. Eventually, the swarm departs for the location promoted most vigorously.