I have been asked many times to provide a "hatch guide" for the Millers River. In short, there is no hatch guide for the Millers. Here's the reason: The Millers is very much like many freestone rivers in central New England. The flies that you find on the Millers are very much the same as the flies that you encounter on other central New England rivers. The hatch times are pretty much the same as on other central New England rivers. Now, our fly boxes are loaded with every creation to "match the hatch" as the saying goes, so why worry! If there are hendricksons hatching we have the right fly. If it's March Browns, Sulphurs, or BWO's we have that too for every stage. In short, worrying about hatches is a fools game. We have enough flies to match what's happening, period!
If you want to have a "guide" to the important insects then buy Tom Ames " Hatch Guide For New England Streams". That is all that you will need.
Here are a few pointers: The Millers is loaded with Hendricksons BUT they are a minor event. I have seen the river loaded with them but with no rising fish. So have the Harrison Brothers who claimed that their paddles drowned hundreds of these flies without seeing a trout rise. The great rod maker Dan Trella says the same thing about the Quaboag River - lots of Hendricksons but no rising fish. Last year's low water brought a great hatch at the Kempfield with RISING BROWNS but it was a rare event.
March Browns - This large fly is a standby from mid May through late June. It's always there and brings the evening fish to the surface. Any March Brown pattern will work if the presentation is correct.
The "Tan Flies" - Sulphurs, Cahills, you name them. They can be all over the river at times from late May through September. ANY tan pattern will work ( I know this from experience)if the size and presentation is right. Sizes 14 through 18 will fill the bill in most occasions.
Caddis - Don't go crazy with the array of surface/sub surface patterns that are out there. Caddis patterns, for the Millers, work best in the top six inches on the water column. My Moby Dick Wet pattern has been doing the trick over caddis water for years as long as the presentation is right. I hardly fish a dry caddis anymore!
In short, don't fret too much over what's hatching. You probably have enough of the right flies to be successful. The again there's always the wooley bugger!!!