Japanese Beetle (Popillia japonica)

Terrestrial, hatching July–August, active in water between 60 and 80°F, and imitated at #12–16. Recorded from the Virginia mountains, where 796 Virginia rivers on this site carry a page.

An introduced beetle with a metallic green thorax and copper wing cases, abundant in agricultural and suburban valleys from July, and peaking through July and August. It is hard-shelled, heavy, and a poor swimmer: the adult sinks the moment it lands, so it is fished in the film or just under, tight to the bank. Only that adult stage concerns a trout. The active water-temperature band runs 60 to 80 degrees, covering cold-transitional, cool and warm classes, and hook sizes are 12 to 16. Where there are grapevines and overhanging brush there are beetles in the water, which is as fine a description of the right water as the records support — the regions here span southern and northern lower Michigan, the Wisconsin driftless, and the Virginia and North Carolina mountains, without naming any particular stream. A Japanese Beetle pattern at 12 to 16 is the direct match; a Foam Beetle at 12 to 18 or a Chubby Chernobyl at 8 to 14 covers the same job.

#12–16Hook size
60–80°FWater, active
Jul–AugPeak months
1Life stage fished

Subbasins with trout water where it is on record: 29 of Virginia's 53.

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

What it is

Terrestrial · Popillia japonica · adult

An introduced beetle with a metallic green thorax and copper wing cases, abundant in agricultural and suburban valleys from July. Hard-shelled, heavy, and a poor swimmer.

Where there are grapevines and overhanging brush there are beetles in the water. Fish it tight to the bank.

When it hatches

Peak is July–August. 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.

60°F 80°F

Active from 60°F to 80°F. On this map that is cold-transitional, cool, warm 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
adult	Sinks the moment it lands. Fished in the film or just under, tight to the bank.

Matching flies

3 patterns in this book imitate the Japanese Beetle, 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.

southern lower Michigan MI
northern lower Michigan MI
the Wisconsin driftless WI
the Virginia mountains VA
the North Carolina mountains NC

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.