Frangipani Caterpillars are also called Frangipani Worms or Frangipani Hornworms because of the spike on their rear end.
They start out by hatching from eggs laid on the underside of the leaves of frangipani trees or sometimes allamanda bushes.
They grow quickly. Their skin is not flexible so they shed their skin as they grow. They may molt five or six times before they reach their full size.
Being that the sap of the frangipani is poisonous to most animals including human beings, the frangipani caterpillars have no enemies. Their bright color serves to warn potential predators not to indulge.
Meanwhile its been my experience that they will eat every last flower and every last leaf on the tree before they fall off and begin the next stage of their development.
The tree does not die, however, and new leaves will grow back. Looking under the tree are copious quantities of small black pellets that could only be caterpillar poop and my guess is that this fertilizes the tree to stimulate the next cycle of growth.
The caterpillars eventually fall off the tree and become become pupae, encased in a shell. Given time they will incubate and become large moths.
The moths also serve to help the tree grow back by acting as pollinators.