Yes the green hard to see caterpillars i think are the most common and have damaged my tomato plants a little bit before i caught them. You have to look at every inch of your plant thorougly because they can hide anywere and not be seen. I found a little green worm under my pepper plants leaf one time (not sure what it was) but havent seen them since. I just recently started seeing my tomato plants stems turn hollow so i looked it up and there is a different type of caterpillar that will make entry into the stem of your tomato plant and will eat it from the inside. I had to throw my plant away because it was completely hollow and dead. I also had a watermelon plant which did really good until it started getting infested with melon aphids on the backside of the leaves. I heard that lady bugs are really beneficial for your garden and they say an adult lady bug will eat up to 5000 aphids in its lifetime. I will try this method and will post how it works but i seen someone post about wasps helping with problems in their garden and would like to know more about how the wasps work.

I use a BT spray once a week as soon as I start getting green tomatoes and that seems to prevent the caterpillars from eating them. The first year I grew tomatoes they ate holes in most of them but I've used the BT every year since with no problems. It is an organic pesticide that only works on caterpillars. The kind I buy is a concentrate that you mix with water. There is also a powder but I find it messy-looking and harder to apply than the spray.

Thank you so much for the quick answers. I don't think it could be snails or slugs, i never see them here in the desert, maybe mice or rats...... but do they climb tomato plants planetes? here is another picture of damage done to an unripe green zebra: https://picasaweb.google.com/candisgood/20110709#5627554021996401058

My husband has the same problem with his tomato plants-$%^& squirrels! He complained to a farmer about it, and was told there's no way to keep squirrels away. They can jump 15 feet. The only suggestion was to build a cage completely around your garden. Include a door for yourself, of course. unfortunately, my DH is not a DIY-type.