How do insects orientate themselves when they fly in the night? They try to keep a constant angle, say [math]\alpha[/math] between the direction of the flight and the direction to some light source. They also keep a constant angle [math]\beta[/math] with the direction “down-up”. [br]When the light source is very far away (like the moon), the light rays are practically parallel and the flight is on a straight line. When the light source is a light bulb, the rays are radial and the flight is on a conchospiral (see reference).[br]Assuming the light source is at the origin of the coordinate [math]xyz[/math]-system, and above the insect when it starts flying, we can describe the initial position of the insect by the vertical distance to the source[math] (z_0<0)[/math] and angle [math]\beta[/math].[br]The trajectory is a conchospiral winding on a cone with a vertex at the light source and opening of [math]2\beta[/math]. The trajectory cuts the light rays on the surface of the cone at a constant angle [math]\alpha[/math].