Yes, they can do a lot of damage. Squish it while it's still small. The little white dot may be an egg, so get rid of that, too.

What kind of bug is it? Do you know? Thanks in advance to anyone that may answer.

I don't mind sharing my tomatoes with the Sphinx moth caterpillers. All these beautiful flying jewels, I consider their caterpillars 'good'!

Rather than snuffing their lives out you can find another suitable hostplant and transfer it there. Live and let live! Some bugs that cause physical harm or discomfort; I kill those, mosquitoes, houseflies, horseflies, deerflies, ticks, chiggers, ect, ect. They're just user/opportunist bugs. They don't care about you, they just want your blood.

It isn't a Hornworm, so don't panic! Hornworms do turn into magnificent moths, but oh the damage they can do!

I wouldn't worry too much about that caterpillar as long as there aren't lots of them. He won't do much damage and at least he won't eat the whole plant, tomatoes and all, like a hornworm would!!!!

Thanks all. I was worried about the exact thing. I didn’t want it to be a tomato hornworm. I read the damage they can cause will wipe out both my tomato plants. I tossed them in the trash, leaf and all.

Do you have a bird bath? That's where my caterpillars go when I find them; the birds love finding them there and even look for them.

I do not have a birdbath but I do feed the sparrows in the front of my house in the morning so maybe they do find them. I do not have the space for a birdbath. My neighbors would flip. They don’t care for me feeding the birds now.I trimmed my tomato plant yesterday for the first time and I didn’t see anything but tiny ants. I will keep looking in the morning and after work every day. Thanks for the help.

Hornworms are the size of fingers, and they have a spike (horn) on their butts. They are hard to miss (except for being the same green as tomato leaves of course LOL) And they are nasty, they spit/poop brown juice when in danger. The best way to find them is either a blacklight at night, or spray the plant with a hose, they wiggle at the cold water.
I just use scissors to cut them in half on the plant, and leave it as a snack for the birds ( but not overhead--see comment above about spitting :) )
Carla in Sac

I have two kinds of worms, Hornworms and Cabbage Moth worms. Yours looks like the 2nd as even tiny Hornworms have the spike.

I love Rhizo_1’s idea of putting them in the bird bath. Caterpillars of all varieties are crucial for birds raising their young. It can take several thousand caterpillars to raise one hatchling to fledgling size. Baby birds can’t eat seeds or fruit, so depend entirely on insects, worms and caterpillars that their parents can bring back to them. Many birds raise two or three clutches of eggs each summer, so they are always in need of live food. Even if you don’t have space for a formal bird bath, you could set a bowl of water on the ground near the tomato plants. It’s even possible the birds might start finding the caterpillars on the tomato plants and save you having to remove them.

Martha