Little caterpillars on tomato plants?

there are little caterpillar looking worms on my tomato plants and i have no clue how they get there my patio is screened in so no moths can get in. i checked google but all i could find was stuff about some green worms the worms im dealing with are brownish and are about 5 cm long. they eat the leaves and the stem of the plant. oh and the tomato plants are in pots and already about 2 ft tall