Snowbush Under Attack by Spanworm
Calls are pouring in about something that is totally stripping the leaves off the plant called Snowbush (Breynia nivosa). If you look closely you will find a yellow caterpillar with black stripes happily munching on the Snowbush leaves. This is the caterpillar or larval stage of the white-tipped black moth (Melanchroia chephise). This caterpillar is a member of the “inchworm” family of moths, also known as “spanworms”.
The moth (adult) is a daytime flyer, which is very unusual for moths. Most moths fly at night. The moth has a wing span a little over an inch with velvety looking wings. The wings are navy-blue to black and have white tips on each of the four wings. Their thorax is orange.
Moths and butterflies are very specific about which plant they choose to lay their eggs upon. For the white-tipped black moth, its favorite plant is the Snowbush. It will also use the Otaheite gooseberry (Phyllanthus acidus), snow-on-the-mountain (Euphorbia marginata) and possibly white sapote (Casimiroa edulis) for its egg laying.
The caterpillar (larva) that emerges from the egg is an eating machine and will soon devour the leaves of the plant. If there is a shortage of leaves the caterpillars may even start feeding on the twigs and bark. Host plants will usually recover from caterpillar feeding, but if there are too many caterpillars and no predators to eat them, they may kill the plant.
What to do: If you enjoy the moth and caterpillar for their unusual beauty you don’t have to do anything.
If you don’t like your snowbush looking tattered or completely lacking in leaves then you will need to kill the caterpillars. The best way to do this is to regularly go out and look at the undersides of the snowbush leaves. Look for salmon-pink eggs (smash them) or for the already hatched caterpillars. You may also notice that the leaves are starting to have chew marks.
When the caterpillars are small you can spray them with an insecticidal soap or use a Bacillus thuringiensis (B.t.) product such as Dipel® or Thuricide®. If it rains, you will need to reapply the product. A spinosad containing insecticide can also be used. Many times if you catch the infestation early you can just prune off the tip branches were most of the caterpillars are located and dispose of them.