Frangipani Caterpillars, Aposematism, and Mangrove Cuckoos

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I have this native frangipani tree growing right below my deck. The tree has been there quite some time, evidenced by a rusted piece of wire fencing that had grown into the trunk and now sticks out on both sides of the tree, indicating that this was a mature tree when Chocolate Hole was still used for grazing animals. My guess is seventy to a hundred years old.


But why not? Native frangipanis grow and flower in the most inhospitable environments on St. John. They grow slowly, recover quickly from windstorm damage and, as far as I know, only have one significant enemy outside of people.

Frangipani Caterpillar

I’ve watched this tree since I’ve been living here, waiting for it to produce bouquets of sweet-smelling, white flowers on the top branches of the frangipani tree, which could be seen directly at eye level by someone standing on the deck. But, alas, so far, this has never happened. Every so often, especially in the spring, the leaves on the tree grow back lush and green, and the flowers begin to bloom.

That’s when the attack begins because along comes this army of caterpillars that quickly devour every last flower and leaf on the tree. The frangipani survives anyway, and the tree makes new leaves and new flowers whereupon arrive the caterpillars, and the cycle begins once again, and so on.


The culprit is the frangipani caterpillar, a brightly colored fat black bug with iridescent yellow stripes and a redhead, and red legs. It’s called a frangipani caterpillar because it only eats the leaves and flowers of the frangipani tree, although I have seen them also go to work on Alamandas and even the highly toxic oleander.

The caterpillars have a voracious appetite. They start off relatively small but get big and fat fast. They can eat an entire leaf in a few minutes, so it’s not long before there are so many caterpillars that they look like black and yellow flowers, and not long after that, there’s nothing left on the tree but bare branches, the caterpillars going off to change into moths somewhere.

This year I intend to go to up against these bugs.

So far, I have been winning the preliminary battles easily without even having to resort to chemical warfare. The tree is not that tall, and I’m able to knock them down using that handy multipurpose St. John tool, a forked stick.

Once they’re down, I’m faced with a moral dilemma, what to do with them.

End them? Easy enough, they don’t run very fast.

But I do happen to be impressed by those bright, beautiful colors, and the thought of squishing them underfoot with their guts just about bursting with green, gushy, chewed-up frangipani leaves seems like it may be somewhat, how should I put this, disgusting.

So far, there haven’t been that many caterpillars to deal with, so I simply bring them somewhere else, away from the tree, in hopes that they’ll get lost or and not be able to find their way back. They will, however, have all the time they want because they have no natural enemies.

Birds and any other predators that normally would eat caterpillars stay away from the Frangipani Caterpillar, whose guts are oozing with poisonous frangipani sap, warned by the bright colors. This defense mechanism is called “Aposematism,” a warning, usually in the form of bright, vibrant colors, to a potential predator that there would be some problem associated with going after that particular prey.

Mangrove Cuckoo

There is an exception to every rule, and this particular exception takes the form of the fairly rare mangrove cuckoo.

The cuckoo gets around the poisonous guts by slapping the caterpillar against the trunk of a tree until there are no guts left.

Having accomplished that culinary preparation, the cuckoo will dine on the frangipani caterpillar, whose aposematism didn’t quite do the trick.

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