Io Moth Caterpillar Identification Guide
A bright green caterpillar covered in branching spiny tufts, with a pale and maroon stripe running along each side.
Read the full Io Moth Caterpillar encyclopedia entry →
Key Visual Features
The io moth caterpillar is a vivid, eye-catching species that grows to roughly 2 to 2.5 inches long.
- Color: Bright lime to apple green body
- Spines: Covered in numerous branching, star-shaped clusters of stiff spines arranged in rows along the back and sides
- Stripe pattern: A pale white or cream stripe runs down each side of the body, bordered below by a reddish-maroon or purplish line
- Body shape: Plump, cylindrical, tapering slightly at both ends
- Head: Small and green, mostly hidden by the spiny body segments
Where and When You'll See It
Io moth caterpillars feed on a wide range of trees and shrubs, including willow, elm, maple, and many garden plants, making them easy to encounter almost anywhere with deciduous vegetation. They are most visible from mid to late summer into early fall. Young caterpillars hatch in tight clusters and feed side by side, giving groups of small orange-and-black early-stage larvae a very different look from the solitary bright green late-stage caterpillars most people picture. As they mature, individuals disperse and are usually found alone on leaves and stems.
Similar-Looking Bugs
- Saddleback caterpillar: Also spiny, but has a distinctive brown "saddle" marking on a green patch, and a much shorter, stockier body
- Other stinging slug and flannel moth caterpillars: Generally lack the paired pale and maroon side stripes and branching star-shaped spine clusters of the io moth caterpillar
- Luna or polyphemus moth caterpillars: Both are green but are smooth or only lightly bristled, without the dense branching spine clusters of the io moth caterpillar
Quick ID Checklist
- Bright green, spiny caterpillar about 2 to 2.5 inches long
- Branching, star-shaped spine clusters covering the body
- Pale stripe with a maroon or reddish line running along each side
- Young larvae found in dense feeding groups; older ones solitary
- Present on a wide range of trees and shrubs in late summer
Frequently asked questions
How do I recognize an io moth caterpillar?
Look for a bright green, plump caterpillar covered in branching, star-like spine clusters, with a pale stripe bordered by a maroon line running along each side of its body.
Do io moth caterpillars look different when they are young?
Yes, young caterpillars are smaller, more orange or reddish with black markings, and feed together in tight clusters, while mature caterpillars turn bright green and spread out to feed alone.
What plants host io moth caterpillars?
They feed on a wide variety of trees and shrubs, including willow, elm, maple, and many ornamental and garden plants.
Can the spines on an io moth caterpillar prick if touched?
Yes, the stiff branching spines can prick on contact, so it is best to observe this caterpillar without handling it directly.
Io Moth Caterpillar identified by the community
Recent Io Moth Caterpillar finds identified with Bug Identifier.
