Button Insect Mystery

hatched insect larvae
You might remember in the past I found two hard, white, button like things on rocks. One on the gorge wall and another on a river rock. I never saw what happened with those two, however the other day I found one on a squash in the garden. Yesterday I checked on the button and crawling out from it were a lot of really small worms. Later in the day I checked again and there were no traces of the worms. They're probably tucked away somewhere eating on the leaves of the plant.