They would probably have to guess, but start here https://en.wikipedia.org/wiki/Polarization_(waves)

> Many animals are capable of perceiving some of the components of the polarization of light, e.g., linear horizontally polarized light. This is generally used for navigational purposes, since the linear polarization of sky light is always perpendicular to the direction of the sun.

You can wear polarized sun glasses to help block the light reflected off of roads and water like when driving or boating. Seeking stronger horizontally polarized light would historically lead you to a water source. Adult horsehair worms complete their life cycle in water.