March Brown hatches take place during the spring months, a popular fly at this time of year with fly fisherman, yet they don’t hatch everywhere. This aside however, March Browns still prove an extremely successful and popular pattern for fisherman even if they are not fortunate enough to witness hatchs in their area.
There are three important stages in their lifecycle; nymph, emerger and dun. It’s important to know each stage and look at how the fish are behaving on the day during a hatch period in order to determine what type of pattern you need to imitate.
Flies start their journey as nymphs, aquatic creatures which can live up to several years before they emerge. During this time they tend to stick close to and hide behind rocks and stones where they are mostly protected from predatory fish.
During March and April, trout are accustomed to seeing nymphs in the water, so if emegers are not hatching into duns, nymphs are the natural choice.
Emergers occur when nymphs rise to the surface and hatch into a dun, a dry fly on the surface of the water ready to fly away. It can take several minutes after the hatch before they are able to fly.
On light dry breezy days, the hardening of the wings happens quickly and the fly escapes the water before trout can take full advantage of the feast. On such occasions you might notice that the fish ignore duns on the surface of the water, and instead target the nymphs as they race to the surface to emerge, so be sure to read the conditions.
The Dun is the sub-imago stage at which the insect develops wings and is able to fly, yet some require a further moult to enter the final imago stage of becoming sexually mature.
Once Duns are on the surface, it’s only a matter of time before their wings are strong enough to fly away. During this vulnerable period, they protect themselves in numbers where countless duns will collect in currents and slack areas on the surface. Trout take it in turns to rise and feed on this abundant source of food in swift strikes, but there are far too many hatches for the fish to eat them all, and many escape and go on to mate.
Jinglers can work extremely well when trout are feeding on duns.
This final stage of their lifecycle is extremely short, for some species only minutes, for most just a few hours. Once fully mature, their sole purpose is to mate, after which they will die. For this reason they do not even have digestive systems!