the insect is a leaf miner. the little guy gets in between the two layers of the leaf and creates what are called galleries. thrips are piercing/sucking insects. their damage resembles spider mites.you may have caught a few miners if your plants were outdoors. you may yet catch them if they are still there. contact pesticides are not really effective. there are only one or two anyway.
edit: you can catch them if they haven't exited the inside. use your finger nails and go to where there gallery ends and dig them out.