Light Cahill (Maccaffertium ithaca)

Mayfly, hatching June, active in water between 55 and 68°F, and imitated at #12–16. Recorded from southeast Minnesota, where 99 Minnesota rivers on this site carry a page.

#12–16Hook size
55–68°FWater, active
JunPeak months
4Life stages fished

Subbasins with trout water where it is on record: 5 of Minnesota's 72.

See Minnesota's trout water on the live map → Every reach coloured by water temperature — the water these hatches come off.

What it is

Mayfly · Maccaffertium ithaca · nymph → emerger → dun → spinner

A cream-to-pale-yellow mayfly with faintly mottled cream wings and two tails. The nymph is a flat-bodied clinger, mottled brown, with sprawling legs.

A cream-yellow evening mayfly on freestone water, running from the tail of the Hendricksons into midsummer. The nymph is a flat-bodied clinger, so it is worth fishing tight to rock rather than in open current.

When it hatches

These are Minnesota's own dates, not this site's shared calendar. They are the Light Cahill (Maccaffertium ithaca) row of Hatch Chart for Southeast Minnesota Trout Streams, Minnesota Department of Natural Resources, Lanesboro Area Fisheries (Vaughn Snook, Assistant Fisheries Supervisor), as of 15 June 2016. The chart's calendar runs January to October and makes no claim about November or December. Its own footer says it is a general time frame, that some streams have only a few of these hatches, and that others may see hatches it does not list.

Peak is June. The pale months either side are the shoulder — the app widens a peak by one month in each direction and recommends the bug there, and no further: that widening is bounded so that a bug peaking in May is never offered in August.

JFMAMJJASOND

peak shoulder not recommended

Water conditions

The band is a water temperature, not an air temperature, and it is the range in which this insect is worth fishing — for a mayfly that is the emergence window; for a scud or a midge it is simply the range trout will still eat one in.

55°F 68°F

Active from 55°F to 68°F. On this map that is cold, cold-transitional, cool water — the band crosses 2 of the three breaks the river colours use. Breaks at 58, 64 and 70°F.

Stages

What the insect is doing, and what that means for what you tie on.

Stage	What it is
nymph	Clings to the sides and tops of rocks in moderate to fast current. Fish it tight to the rock rather than in the open channel.
emerger	Comes off through the surface in the evening, quickly in warm water. A film pattern matters less here than in the smaller hatches, but it still helps in flat runs.
dun	Pale and conspicuous at dusk, and the reason 'a Cahill' is what half the fly boxes in the East have in June.
spinner	An evening fall with the wings flat on the water; the body goes from cream to a deeper tan as the fly dies.

Matching flies

4 patterns in this book imitate the Light Cahill, across its stages. Which one to tie on follows the stage the water temperature says it is in — the app makes that call on a live reading; this page lists the whole set.

Where to find it right now

The rivers with a page here that sit in this insect's regions, with a USGS gauge reporting water temperature. This list is re-ranked against the reading each gauge is sending now and today's date, so it is live — the fallback below it, if the readings do not arrive, is each river's measured July mean.

Regional presence

Regions, not collection records. This insect is recorded from the coarse regions below; nobody has surveyed which named river it has been caught on, and this page will not pretend otherwise.

northern lower Michigan MI
southern lower Michigan MI
the Upper Peninsula MI
the Wisconsin driftless WI
northern Wisconsin WI
the Virginia mountains VA
the North Carolina mountains NC
southeast Minnesota MN

Rivers in these regions with a page here

Related hatches

Same family, or overlapping this one's calendar on the same water.

Open the trout map →Every trout stream near you, coloured by today's water temperature.