What is this?
While I recognize this caterpillar, I am curious as to what plant it is feeding on? it looks like it might be tomato.
Your caterpillar is a hornworm whose adult moth is commonly known as the white-lined sphinx, Hyles lineata. Your caterpillar is a dark form (there is a lighter form) and the color variation may be related to what the larvae is eating. One of my resources below does indicate the larvae will feed on leaves of tomatoes and grapes.
Below are a couple references that discuss this particular species of hornworm or sphinx moth:
Hope this helps!