Could you be referring to hornworms? They are green, the same color as the tomato stem and leaves, and very difficult to spot. If they are, get them off ASAP since as they mature very quickly, they eat a lot of the plant quickly. I pick them off and stomp on them. I did eventually have a cardinal that would "guard" my tomatoes and eat the hornworms, but it was years to happen. I don't use pesticides on my vegetables, so I'm not sure how to apply, but BT is an effective organic method to eliminate caterpillars.

thanks for responding. They aren't green caterpillars. I'll try and paste a picture in this. What is BT?

Thanks for the info,I dont want to kill any bees... there must be another natural solution

Only the one type of BT kills honeybees according to the national peticide information center. Google that site for more info.

BT sold as caterpillar killer will not kill bees. In fact, it won't harm anything except caterpillars, which is why it's such a great pest control solution.