Polyphemus Moth Caterpillar Identification Guide
A large green caterpillar with faint diagonal lines and small silvery, reflective spots along its sides.
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Key Visual Features
The polyphemus moth caterpillar is a substantial green caterpillar that reaches about 3 to 4 inches at full growth.
- Color: Bright to medium green body
- Diagonal lines: Faint pale yellow diagonal lines run along each side, one per segment, similar in placement to the tobacco hornworm but much less bold
- Reflective spots: Small silvery or metallic-looking spots dot the sides of the body, a feature fairly unique among green caterpillars
- Tubercles: Sparse small reddish-orange tubercles, each with a few short bristles, positioned along the back and sides
- Body shape: Thick and cylindrical, tapering slightly toward the rear
- Legs: Three pairs of small true legs near the head plus fleshy prolegs supporting the rest of the body
Where and When You'll See It
Polyphemus moth caterpillars feed on a broad range of hardwood trees, including oak, maple, birch, and hickory. They are most often encountered from early summer through early fall, feeding on leaves and resting along twigs and branches during the day. Their green coloring and stillness make them easy to overlook against foliage until a chewed leaf edge or dark, ridged droppings on the ground below give away their presence.
Similar-Looking Bugs
- Luna moth caterpillar: Similarly pale green and large, but shows small yellow dots rather than diagonal lines, and lacks the silvery reflective spots
- Cecropia moth caterpillar: Larger and heavier bodied, with prominent large coral and yellow knob-like tubercles instead of small red bristled tubercles
- Tobacco/tomato hornworm: Also green with diagonal markings and a similar body shape, but hornworms have a distinct horn at the rear end, which polyphemus caterpillars lack
Quick ID Checklist
- Large green caterpillar, about 3 to 4 inches long
- Faint pale diagonal lines along the sides
- Small silvery, reflective spots on the body
- Sparse small red tubercles with short bristles
- No rear horn (helps separate it from hornworms)
- Found on oak, maple, birch, or hickory leaves
Frequently asked questions
What is the best clue for identifying a polyphemus moth caterpillar?
Look for small silvery, reflective spots along the sides of an otherwise plain green body — this feature is distinctive compared to most other large green caterpillars.
How is a polyphemus moth caterpillar different from a hornworm?
Both are green with diagonal side markings, but hornworms have a noticeable horn projecting from the rear end, while the polyphemus caterpillar does not.
What trees do polyphemus moth caterpillars feed on?
They feed on a wide range of hardwoods, commonly including oak, maple, birch, and hickory.
When are polyphemus moth caterpillars most commonly seen?
They are most often spotted from early summer through early fall, resting on leaves and twigs of their host trees.