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Inchworm (Geometridae)
Terrestrial, hatching May–June, active in water between 50 and 68°F, and imitated at #12–16. Recorded from northern lower Michigan, where 459 Michigan rivers on this site carry a page.
A small green geometrid caterpillar that lowers itself from overhanging branches on a thread and, often enough, into the water. Bright chartreuse, an inch long, and entirely out of place in a fly box until May. Only the larva matters, and it is fished tight under overhanging cover on small, brushy, tree-lined water — a green weenie is not a joke pattern in inchworm season. The peak is May and June, in water from 50 to 68 degrees, a band covering cold, cold-transitional and cool streams, at hook sizes 12 to 16. It drops off hardwood canopy into small mountain streams all spring, and on Appalachian brookie water it is close to a cheat code. A Green Weenie or Green Caddis Larva, both 12 to 16, is the direct imitation; a Foam Beetle at 12 to 18 covers the same water when something bulkier is wanted. The regional records run across the Virginia and North Carolina mountains, northern lower Michigan and the Wisconsin driftless.
- #12–16Hook size
- 50–68°FWater, active
- May–JunPeak months
- 1Life stage fished
What it is
Terrestrial · Geometridae · larva
A small green geometrid caterpillar that lowers itself from overhanging branches on a thread and, often enough, into the water. Bright chartreuse, an inch long, and entirely out of place in a fly box until May.
Drops off hardwood canopy into small mountain streams all spring. On Appalachian brookie water it is close to a cheat code.
When it hatches
Peak is May–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.
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.
Active from 50°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 |
|---|---|
| larva | Fished tight under overhanging cover on small, brushy, tree-lined water. A green weenie is not a joke pattern in inchworm season. |
Matching flies
4 patterns in this book imitate the Inchworm, 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.
- Foam Beetle terrestrial · #12–18 — Black foam, a bit of flash on top. The most reliable summer dry on wooded streams.
- Foam Inchworm terrestrial · #12–16 — A length of bright green foam and nothing else. Cast tight to overhanging hardwood; the natural arrives from above, not from upstream.
- Green Caddis Larva nymph · #12–16 — Bright green free-living larva. In the drift twelve months a year.
- Green Weenie nymph · #12–16 — Chartreuse chenille. Appalachian brook-trout water does not have a better fly in June.
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.
- Baldwin River northern lower Michigan · July mean 61.3°F
- Beaver Creek northern lower Michigan · July mean 61.3°F
- Bray Creek northern lower Michigan · July mean 61.3°F
- Coe Creek northern lower Michigan · July mean 61.3°F
- Diamond Lake Outlet Creek northern lower Michigan · July mean 61.3°F
- East Branch Hersey Creek northern lower Michigan · July mean 61.3°F
- East Branch Pine River northern lower Michigan · July mean 61.3°F
- Hersey Creek northern lower Michigan · July mean 61.3°F
- Hoxey Creek northern lower Michigan · July mean 61.3°F
- Johnson Creek northern lower Michigan · July mean 61.3°F
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.
- the Virginia mountains VA
- the North Carolina mountains NC
- northern lower Michigan MI
- the Wisconsin driftless WI
Rivers in these regions with a page here
- Au Sable River
- Muskegon River
- Acme Creek
- Adams Creek
- Addis Creek
- Alabaster Whitney Drain
- Allen Creek
- Anderson Bayou
- Antler Creek
- Antrim Creek
- Apple Creek
- Asum Creek
- Atkinson Creek
- Au Gres River
- Au Sable Creek
- Backus Creek
- Baker Creek
- Bakers Creek
- Baldwin River
- Bamfield Creek
- Barger Creek
- Barker Creek
- Barker Creek
- Bartholomew Creek
- and 435 more
Related hatches
Same family, or overlapping this one's calendar on the same water.
- Caterpillar Lepidoptera larvae · Terrestrial · May–September
- Periodical Cicada Magicicada spp. · Terrestrial · May–June
- Black Ant Formicidae · Terrestrial · June–September
- June Bug / Beetle Phyllophaga spp. · Terrestrial · June–July
- Leafhopper Cicadellidae · Terrestrial · June–September