Q. I have an older, very large royal poinciana in my swale that is shedding leaves and little black droppings for the past month. In my 15 years in my home, the tree has never done this and I noticed that some nearby poincianas are doing the same thing. What’s going on?
T.S., Miami Beach
Your royal poinciana is infested with the royal poinciana caterpillar ( Melipotis acontioides), a species of a moth. There is little evidence that the tree is harmed but the caterpillars should be controlled.
The royal poinciana caterpillar hides during the day in debris at the soil surface near the base of host trees. It is a nocturnal feeder and soon after dusk they can be seen racing up the tree trunk in “herds”. It can be alarming to see thousands of caterpillars moving up the tree trunk and devouring the leafy canopy. You can hear their droppings hit the ground as they feed.
This species of caterpillar feeds almost exclusively on royal poinciana, although it has been reported to also eat the foliage of Jerusalem thorn. They can be found throughout much of the year, but people report seeing the leaf feeding during summer and fall.
Apparently outbreaks are infrequent, happening every 10 to 15 years or so. The mystery remains as to why there are such long periods between outbreaks and why the damage has occurred in different months and only on select trees. Certain trees seem to be targeted and defoliated while nearby trees have very little or no feeding damage.
You can stop the caterpillars by wrapping a piece of cloth folded into loose layers around the trunk of the tree in a band. This fabric band will trap them. The hiding caterpillars can easily be removed by changing the band on a regular basis.
A predator of the royal poinciana caterpillar is the paper wasp. These wasps can sometimes be seen searching tree trunks and feeding on caterpillars that are not well hidden in their daytime resting places.