I never connected them with the early to mid-summer waves of caterpillars that look like bird droppings and defoliate our potted citrus trees if I don't remove them promptly.
After picking close to a dozen of them off the tangerines and lemon over the weekend, I turned to Google for help in identifying them. What's That Bug has a photo of them identified as "orange dogs" about a third of the way down this page. Turns out they're the larva of the giant swallowtail (Papilio cresphontes).
I will continue to pick them off my citrus trees but I feel better knowing what they are.