Newly hatched larvae are clear yellow, and in the second instar assume their green coloration.
The larva is green with two grey stripes bordered in cream along the sides and the horn at the rear end typical of sphingids. The horn is purplish red, changing to blue with an orange tip in the last instar. They feed fully exposed on the top of the host plant and rest in among a tangle of stems. Although dependent on warmth and sun, the larval stage can be as rapid as 20 days.
This site contains all information about Hummingbird Hawk Moth Caterpillar.