12 Sun Compass Navigation

Key Idea: The position of the Sun is an important navigational cue for many animals including insects such as bees and ants. Honeybees navigate using a sun compass, so honeybees communicate the direction and distance to food relative to the current position of the Sun. In the waggle dance, they adjust their dance to account for the changing direction of the Sun. Animals that see polarised light can detect the plane of light in the sky even if the Sun itself is obscured from view.

The honeybee waggle dance

In bee hives, the combs hang vertically.

Position of the Sun

The vertical axis of the honey comb equals the current position of the Sun.

Other bees will be in close attendance to monitor the dance and learn the location of the new food source. 40°

Food source

Movements of the bee to the left and right of the vertical axis give the angle of the food relative to the Sun. In this case the food source is 40° to the right of the Sun. 3D

If the bee moves directly up the comb, it means the food source is directly in line with the Sun. The duration and speed of the waggle indicates how close the food source is. A long dance indicates a more distant food source. A faster waggle indicates a richer food source.

Bees communicate the direction and distance of the food source through the waggle dance (above). If food is located directly in line with the Sun, the communicator (bee in the blue circle) demonstrates it by running directly up the comb. To direct bees to food located either side of the Sun, the bee introduces the corresponding angle to the right or left of the upward direction into the dance. Waggle dancing bees that have been in the hive for an extended period adjust the angles of their dance to account for the changing direction of the Sun. This means directions to the food source are still correct even though the Sun has changed positions.

Polarised light navigation in ants

An experiment investigated the effect of polarised light on navigation in Cataglyphis ants by placing a food source at a regular location near a nest. The ants learned its location and moved directly to the food source each foraging trip. A polarising screen was then placed over the ant trail. Rotating the screen caused the ants to follow a path at an angle equal to that which the polarised screen was rotated (right).

Bjørn Christian Tørrissen CC 3.0 Saharan silver ant (Cataglyphis bombycina) Training under clear blue sky Polariser in place Polariser 50° left Polariser 50° right

Direction of travel by ants Angle turned by ant (°)

90 30 120

60 Direction of polarised light

30 90

Polariser angle (°) 60 The direction of travel by the ants is equal to the angle of rotation of the polarised screen.

2. (a) Explain how a honey bee communicates the location of a food source to other honey bees in the nest:

(b) Explain the adaptive value of this behaviour:

3. Explain how the bee compensates for the time it takes between finding the food and delivering its message to the hive:

4. What environmental cue do Cataglyphis ants use to navigate?

5. What was the effect of rotating the plane of polarised light on the ants' ability to navigate to the food source?

6. Diagram A below shows the foraging and return trips of a Cataglyphis ant under blue sky. On diagrams B and C draw in the line of the return trip of the ant when a polarised screen is placed over the ant:

Food source Food source

Foraging trip

Return trip Foraging trip Food source

A

Nest

Foraging under clear blue sky

B

Foraging trip Nest

Polarised screen placed over ant and rotated 25° to the right.

C

Nest

Polarised screen placed over ant and rotated 45° to the left.

7. Explain why animals that can detect polarised light (e.g. ants and bees) can continue to navigate accurately when the

Sun is obscured from view (e.g. a partially cloudy day).