You're wearing gloves in the photo Erin, squish 'em.

I can try but they’re very small, there must be thousands of them, and my hibiscus is quite large with many leaves. Any other suggestions?

I'm not suggesting you pick off each teeny caterpiller and squish it between your fingers. Hold a leaf between your hands and rub the bottom side gently. They squish easily. If you spray an insecticide it's difficult to reach the undersides of the leaves.

Got it - lot of leaves to squish but you have a point about trying to spray it! Is there anything I can do to prevent this from happening next year (and avoid the bug squishing lol)?

I have a Hibiscus and I had the same issue, with caterpillars that I found on the underside that were making a mess of the leaves. I found them very easy to roll off and squish with garden gloves on. Just dragging your hand along the back of the leaves you'd feel the caterpillars. You could turn the leaf over and easily see them too.

My suggestion is to get at it EARLY next year. I just checked my leaves yesterday and I have none so far. The leaves are blemish free and just started unfurling this week. So there is hope, that the more you kill, the less you have in following years.

I had issues in the past with sawfly larvae on dwarf pines. I agree with removing the larvae by hand as early as possible. Put something under the leaf as you do it to catch the larvae that try to drop to the ground. After 2 years, no more larvae problems.

This gives me hope! Thanks all!

Their cousins defoliated my columbines. imagine trying your tecnique on that foliage!

if anyone has please advise

If you are talking about leaf miners, Marie, I pull off any foliage that has them and throw them away. If they are covered with them, I cut it back to the ground and throw it away and it grows back a nice rosette of new foliage. The more you do it, the less you have every year.

@prairiemoon2 z6b MA Columbines are attacked by both leaf miners and sawflies. The leaf miners leave their characteristic "trails" on the foliage, whereas the sawfly larvae defoliate the plants nearly completely. As you pointed out, cutting columbines back after damage is usually pretty effective in getting them to regenerate fresh new foliage.

sah - I've never had sawfly damage to columbines then. Just the leaf miners. I do have the sawflies on the Hibiscus. I haven't seen them this year yet.