Mayflies molt after they hatch. This also occurs on grass and weeds. While you look for clues of a recent hatch, see if any aquatic insects are crawling around on nearby bushes. Streamside brush is a great hangout for aquatic insects that have recently hatched and are waiting their turn in the egg laying cycle. If you see a lot of a certain kind of insect hanging around the brush, you can bet on patterns that imitate that insect when you get to the stream.
Spider webs are a great place to look for clues.
Spiders make a habit of catching insects that fly around their web. If the web is loaded with unfortunate mayflies, the fish are probably loaded with them too. Here s a perfect opportunity to match the size, shape and color of the fly without trying to catch one on the water. If you don t see rising fish, it s not very likely that they ll eat a fly floating on the surface. If you don t see them rising, a nymph might be in order.