That's the caterpillar of the beautiful Giant Swallowtail Butterfly. They are a relatively common pest of citrus country-wide. Plenty of parasites and predators help control them in all stages, but they are capable of munching away at a lot of foliage.

I grow some seedling citrus in containers just for the benefit of the butterflies, but others may not wish to sacrifice their plants that way.

Look for the small, pearl-like eggs laid singly on the leaves, usually the upper surface. Your caterpillar, by the way, is not a youngster. Inspect your plants regularly, if possible, so that you can find them when they are still tiny.

Thank you very much for the ID. I will keep an eye out for damage before I think about doing anything. I have seen several of those butterflies flying around, but never knew what the lavae looked like. Since I tore out my lawn last spring and replaced it with natives, I have seem a lot of things that I have never seen before. Thanks again.

"...I have seen a lot of things I have never seen before."

I'll BET you are, boozer. You may find that you've attracted more of the natural pest control agents, enough so that you see little damage from the caterpillars.

Look for numbers of regular wasps (like the mud daubers), which take caterpillars away to stuff into their muddy egg chambers for the developing wasp larvae. Tiny parasitic wasps are much more difficult to see, but are considered a primary control of caterpillars. There are also predatory stinkbugs (and other members of that family), beetles (even ladybugs will eat the eggs and very young caterpillars), birds, lizards, snakes, tree frogs, squirrels, and more!

Good luck!