What is this on my tomato plants?
This is a very cool larva of the Eggplant tortoise beetle. You can look at photos online. The adult beetle does not have the spines on the side. It is carrying excrement or frass on its back as a disguise.
There is also another tortoise beetle whose larvae is green and eats solanaceous plant, such as tomato, but it matures into a black and clear-paned tortoise beetle. You can see it online too. It does not have a common name, just a scientific name.
We can't say for sure which species of tortoise beetle you have until they mature. Neither is significant enough to control.