Colorful orange, black and white ailanthus webworm moths are beneficial pollinators

A few days ago in the garden, I spotted a small but very attractive insect. It was slim, around three quarters of an inch long and had a striking orange and black pattern that was hard to miss. I have seen these before, they are called ailanthus webworm moths.

In contrast to most moths that hold their wings loosely over their bodies, the ailanthus moth wraps its wings tightly around its body. The close-fitting wrapping makes it looks like the insect has a shell; it could easily be mistaken for some kind of beetle.

Its name is derived from Ailanthus altissma, the scientific name of the tree-of-heaven, which the caterpillar stage feeds on exclusively.

Ailanthus webworm moths are native to Florida were they feed on certain types of trees in the Simaroubaceae family. In the late 1700s, tree-of-heaven was imported from China and planted in Philadelphia. It quickly spread southward toward Florida and eventually reached the range of the existing ailanthus moth population. The moths then moved on to feed on the tree-of-heaven. From that point in time, the moths followed the movement of the tree-of-heaven population as it expanded.

Tree-of-heaven is an undesirable, non-native species of tree that can become very invasive in some locations. It is very adapted to growing in urban and suburban environments. So if you spot one of these colorful moths, you can be sure a tree-of-heaven in not very far away.

Much like monarch butterflies, the ailanthus webworm moths absorb and retain the unpleasant tasting chemicals from their diet causing birds to avoid them.

Like other webworms, the ailanthus webworm caterpillars eat tree leaves by feeding in groups under webbing that they produce as a protective covering. There are more than one generation per season.

While the caterpillar stage feeds on only one species of plant, the adult moth feeds on nectar from all kinds of wild flowers and garden flowers making them valuable pollinators.

Since they eat an invasive species of tree and pollinate many kinds of flowers, they are truly beneficial insects that should be encouraged and not destroyed.

The adult moth flies and feeds during the day as well as the night which sets it apart from most other moths which fly at night. I spotted mine late in the morning, wandering around on a spike of purple loose strife flowers crawling from flower to flower looking for nectar. At the time I was counting the number of species of wild bees visiting the plant.

The moths tend to seek out flowers that have multiple florets. Once they land on a plant it appears that they tend to spend more time crawling to the next floret rather than flying like bees and other insects tend to do. That made it a lot easier for me to snap a photo of it.

I’m always amazed at the beauty and complexity of the natural world.