Fruit flies, like many other insects, use the sun as a reference for navigation. They have specialised photoreceptor cells in their eyes that are sensitive to the position and polarisation of the sun's light. These cells, known as ocelli, are located on the top of their head and send signals to the fly's brain.

Here's how the common fruit fly (Drosophila melanogaster) uses the sun to navigate:

1. Detection of Light Intensity and Direction: The ocelli detect the intensity and direction of sunlight. The angle at which the light strikes the ocelli provides information about the sun's position relative to the fly's body.

2. Polarisation Pattern: Fruit flies are particularly sensitive to the polarisation of sunlight. The light from the sun is polarised, meaning the light waves vibrate in a specific direction. Fruit flies can detect the plane of polarisation of the sunlight and use this information for orientation.

3. Internal Compass: Fruit flies have an internal compass that integrates the signals from the ocelli and other sensory inputs, such as the wind direction and visual landmarks. This internal compass allows them to maintain a consistent flight course and navigate back to their home base.

4. Compensation for Sun's Movement: As the sun moves across the sky during the day, fruit flies adjust their flight direction to compensate for its movement. This is made possible by comparing the current sun's position with their internal compass.

5. Landmark Orientation: In addition to using the sun, fruit flies also use visual landmarks, such as vegetation, buildings, and other prominent features, to aid their navigation. They may use landmarks to refine their flight path and locate resources like food and mates.

Overall, the common fruit fly's ability to use the sun and other sensory cues to navigate allows it to successfully locate resources, avoid predators, and maintain its position in the environment. This navigational capability is essential for their survival and reproductive success.