Hollyhocks in Indiana are commonly attacked by larvae of the Hibiscus Sawfly, Atomacera decepta. Sawfly larvae resemble caterpillars, but with 8 rather than the typical 5 pro-legs.
The adult sawflies lay eggs inside the leaf, producing a blister-like swelling when viewed from above. The larvae hatch and move to the undersides of the leaves to feed. Early instar larvae will skeletonize the leaves, leaving the upper membrane intact. As they grow larger, the consume the entire leaf (except veins) and may feed on the flowers.