Animals help us navigate in lots of ways.
They form both compasses and maps for us.
The map is formed in a similar way to the method we use with plants: if we understand the habitat and ecology of an animal or a plant then spotting it in the wild gives us a sketch of our surroundings. If a dragonfly needs still water for its life cycle and does not range far from it, then spotting it forms part of a basic map: there is still water nearby.
The compass is often found by looking for the footprints of sun or wind.
In the case of spiders’ webs the logic is straightforward: spiders do not construct webs in places that are over-exposed to the wind. If we know where the wind blows from then we can safely assume that more webs will be found on the lee, sheltered side of obstacles than on the exposed windward side.
Like all natural navigation methods there are degrees of sophistication and experience helps. The beginner may look at the top web and start to leap to conclusions about direction. They may be right or wrong, it is worth looking, but in isolation quite a weak clue.
However, with experience we start to notice that the sheltered side of obstacles, like trees, can form favourite spots with spiders. This has two consequences: more webs are spun in that location and more of these webs survive for a long period. Old webs usually collapse and start to look the corner of rooms in horror movies, but they are still recognisable as webs.
Think of gales acting like a spring cleaner, they sweep through the forest sweeping dust, leaves and webs along with them. In sheltered spots, eg. the northeast side of trees in the UK, we find that webs are spared this cleaning and lots of old webs start to gather on the same side. The chances of so many webs all surviving on only one side of a tree grows closer to zero. This is now a more dependable clue.
The webs in the second picture are a stronger clue than those in the first picture. And those in the third picture are screaming direction.