As the first 20 degree days occur in northern Tasmania, the common mayfly begin to become active and the first hatches occur. This can mean some great dry fly action in the early part of the season.
The nymph lives in the water all year round, going through various growth phases known as instars.
Hatches occur when the water temperatures rise above 12 degrees Celsius. From experience the best of these hatches will be on overcast, or even drizzly days, along with some warmth. It is especially the changes of light from say, 10 am through till mid afternoon, that will give rise to the greatest waves of these emerging mayfly.
The nymph, in the right conditions, comes to the surface and struggles free of its casing. These are commonly known as the emerger.
This is often the most vulnerable stage during the hatch and I would tend to use an emerger imitation, preferably with a fine wing, such as CDC, as a go-to fly throughout the hatch. A nymph can also be trailed a few feet behind the emerger for those fish that are just not ready to take off the top.
This is the dun. Once it has broken free of its shuck in the emerger stage, it will fly away to the bank-side vegetation, if it’s not taken by a trout or bird. In a good hatch you will see these popping out of the water in the emerger stage, and they sit on the surface of the water looking like little sailboats and may even be blown around.
When this is happening, I would still tend to use the emerger imitation, but with a good wing.
The trout will gobble up the nymph as it makes its way to the surface and struggles to be free. The trout will not bother with the empty shuck but focus on the emerger trapped in the film on the surface. They may even ignore the full adult (dun) as the emergers are easy pickings for them.
If it starts to drizzle and hundreds of these adults are trapped on the surface and the trout start to focus on the surface flies, this is where I might replace the nymph with a full dry fly imitation.
Once the duns reach the bank, within a couple of days they will go through a final transition into the spinner, or full adult. It’s only purpose is to mate and lay eggs, to then fall spent on the water. This usually happens in calm conditions, or protected areas where they can hover and swarm.
This adds a new dimension to the fly fishing experience because as these insects lay helplessly on the water, the trout will come along and sip many of them down. In these circumstances I would generally prefer one fly on the point, being a sparse, spent spinner.