Sorry i dont have a pic, but someone may know.
Pelargoniums at work are showing holes in leaves, at first it looked like slug grazing but ive caught a couple of small grubs. Id say caterpillar, but which ? or is it another kind of bug/leaf miner. The only other signs are small black eggs, which just look like small compost particles on the leaves.
Ive used the intercept drench which by all accounts kills most things that eat the leaves, but it will take a while to see if this works and the plants recover.
Not sure but I've seen similar small caterpillars on leaves before, the black bits sound like Frass (caterpillar poo)!
???