Hi- these are tortoise beetles, a relatively benigh insect that will chew holes in the leaves of many different garden plants. It's more typical to see them feeding on sweet potato than eggplant. They are using their excrement (black material) to ward off predators.
https://extension.umaine.edu/home-and-garden-ipm/fact-sheets/common-name-listing/tortoise-beetles/

You can hand pick the beetles or spray with spinosad or pyrethrins if they are causing significant injury.
Jon