These larva have surrounded a dogwood leaf in NE Pennsylvania. No others have been found on the tree. They are about 1 1/2 long.
Your beautiful caterpillars are Io moth caterpillars, one member of the silk moth family – Saturniidae.
They feed on a wide variety of plants including birches, clover, corn, elms, maples, oaks, willows, roses, cotton, hibiscus, azaleas, palms, and even some grasses.
They are not a pest.
The caterpillars stay in clusters early on, but will separate as they mature. So would expect yours to head out on their own soon.
They leave the hostplant to form a cocoon, usually in leaf litter. There may be up to four generations in the south, but usually just one in the north.
These insects are found in eastern North America west to AZ.
Caution: The caterpillars may “sting” if handled.
The larger the caterpillar the more intense the stinging sensation caused by the spines. Glad you checked on this one.
Neat to find so many together on one leaf!!