The Value of the Frangipani Worm

It is believed that the coloration of the caterpillars warns predators away as they mistake the caterpillars for venomous Coral snakes

I recently photographed a very large, colorful caterpillar slowly working its way up a wall late one evening.  It was almost five inches long and as thick as my index finger. Its body was banded in brilliant yellow and black rings while the bright red head was partially protected by an orange ‘collar’ sprinkled with tiny black hairs.  Its legs were orange with black spots and, near its tail, there was a black spike approximately one inch long protruding from a raised orange button.

When I was describing it the next day to some islanders in the hopes of ascertaining what sort of moth or butterfly it would become, I was told that it was not a caterpillar but simply a worm, the Frangipani worm, and that I’d made a terrible mistake by not squashing it since it destroyed flowering plants.  Having no intention of ‘squashing’ something that beautiful, and adhering to the principal that we must learn to share our planet with other living things, I set out to discover what the Frangipani “worm” becomes as it proceeds through its four phases of development.

The Frangipani Worm By © Hans Hillewaert, CC BY-SA 4.0
The Frangipani Worm By © Hans Hillewaert, CC BY-SA 4.0

The Frangipani worm, also known as the Frangipani Hornworm due to the spike near its tail, begins life the same as all butterflies and moths—as an egg.  Measuring approximately 8/100 of an inch, the pale green Frangipani worm eggs are laid in clusters of 50-100 on the underside of leaves.  Within hours of hatching, the larvae, or caterpillars, take on the outstanding coloration described above.

It is believed that the coloration of the caterpillars warns predators away as they mistake the caterpillars for venomous Coral snakes.  Predators who do not pay heed to the danger-signaling colors may find themselves sickened or even killed by the poisonous toxins harbored in the caterpillars’ bodies.  Found from Brazil through Central America, the West Indies, and southern Florida, the Frangipani caterpillars feed upon the leaves of dogbane plants including frangipani (or plumeria), allamanda, rubber vine, and the devil’s potato.  These plants produce sap that is toxic to most species, including man, but which the caterpillars are able to ingest without harm.  Scientists studying the Frangipani caterpillars have reported occasional bites when handling the caterpillars as well as some instances of keratitis when hairs from the caterpillars have inadvertently been rubbed into a human’s eyes.

Because the caterpillars do not have a flexible outer skin, they must molt as they grow; sometimes molting as many as five times within a two week period.  Once they have reached their maximum size of up to six inches, the next phase of development takes place as they become pupae, encased in a hard shell which falls to the ground where it incubates in leaf litter or in subterranean burrows.

When first formed the pupae is yellow but within a few hours the pupal covering develops brown spots with darker banding on the abdomen.  As the pupae mature they become brownish red with darker, almost black abdominal banding.

Upon emerging (eclosing) from the pupae, the Frangipani worm becomes the Tetrio or Giant Gray Sphinx moth.  When first eclosed, the moth is helpless and vulnerable as it waits for its wings to dry and become stable for flight.  Females, larger than their male counterparts, have wingspans of over five inches.  While some consider the Giant Gray Sphinx moth to be rather drab and unattractive, closer inspection reveals an intricate wing pattern of camouflaging with black, gray, white, and several shades of brown mixed in fuzzy looking zigzagging lines broken by solid color patches.  Their bodies are banded in gray, brown and white while their heads sport very large black eyes and long white antennae.

Not particularly attracted to light as most moths, the Giant Gray Sphinx moth feeds upon nectar.  Due to their long, needle-like proboscis and the way they hover and dart about when feeding from a flower, they are sometimes mistaken for hummingbirds.  And, like hummingbirds and bees, the Giant Gray Sphinx moth carries pollen from one plant to another thus providing a valuable service.

Seen virtually year-round in Central America except for the months of December and March, the Giant Gray Sphinx moth has been observed in the summers as far north as Pennsylvania as well as states bordering the Mississippi River indicating they may migrate for very long distances.

Although there is no doubt that the Giant Gray Sphinx moth caterpillar, commonly called the Frangipani worm, feeds upon the leaves of ornamental plants such as frangipani and allamanda, experts disagree on the danger they represent to these plants. While the local people I spoke with concerning the ‘worm’ I found on the wall swear that every worm should be killed to prevent the total destruction of decorative plants, entomologists differ in opinions.  Some say the ‘worms’ only eat leaves that are about to fall as a result of the plants’ cyclical shedding.  Others claim that, unless there is a heavy infestation of the worms, only a few leaves will be lost to their feeding.  Still others claim that only a handful of Frangipani worms can strip a 20’ tree bare within a few days.

When we look around our islands and in the gardens surrounding our homes we find many healthy, fully leaved plants.  Sometimes we see the Frangipani worms—but rather than ‘squash’ them, can we not allow them to proceed through their metamorphosis to become the Giant Gray Sphinx moth?  The damage done by the caterpillar is repaired by the moth as it flits from flower to flower spreading pollen, helping to perpetuate many flowering plant species.

Becky Bauer is a scuba instructor and award-winning journalist covering the marine environment in the Caribbean. She is a contributing photographer to NOAA.