Many moths are nighttime feeders but beautiful ermine moths, the adult stage of ailanthus webworms, feed during the day.
With the arrival of pumpkin patches and the Halloween season, it’s time to feature one pretty moth dressed in Halloween colors and one beautiful but dastardly invader, both with a fondness for Tree of Heaven (TOH). First, let’s meet the ermine moth, Atteva aurea, and its larva known as ailanthus webworm. This southern moth made its way north with the arrival of a host plant, TOH from Asia. Many of you may be familiar with Betty Smith’s wonderful tale “A Tree Grows in Brooklyn.” This novel chronicles a young girl’s triumph over childhood hardships and poverty in a Brooklyn neighborhood. The tree that grows in Brooklyn is the irrepressible TOH, Ailanthus altissima, a stalwart thriving in the most dismal of urban environments. In Smith’s novel it serves as metaphor for the girl’s resilience in the face of adversity as she survives the tribulations of childhood. Tree of Heaven hails from Asia but was introduced in 1784 to a garden in Philadelphia. In the United States it now ranges from coast to coast and border to border. Several Canadian provinces have also been invaded by TOH. TOH is reviled as an invasive species throughout much of its range due to its ability to thrive in the worst of sites and to displace native vegetation. In addition to being the host of a drop-dead gorgeous giant silk moth, the Cynthia moth, its woody tissues, leaves, and seeds serve as food for nefarious invasive species including spotted lanternfly and brown marmorated stink bugs we met in previous episodes.
After years of infestation by hordes of spotted lanternflies, Tree of Heaven like these two may succumb to their ancient nemesis from Asia.
What does this segue have to do with ailanthus webworm? Here’s the story. Ranging from the rainforests in Central America to states in the southern US are trees in the plant family known as Simaroubaceae. In the wilds of Florida, glossy leaves of beautiful native Paradise trees, Simarouba glauca, serve as a food source for ailanthus webworm caterpillars. It just so happens that TOH is also a member of the Simaroubaceae. When TOH gained its Philadelphia freedom and moved south and west, it came into contact with other members of the Simaroubaceae. Ailanthus webworm took a liking to TOH and added ailanthus to its carte du jour. TOH now serves as fine dining for these snaky caterpillars that build silken webs on leaves of ailanthus in late summer and early autumn here in the DMV. In several northern states, ailanthus webworms appear late in the temperate growing season. Apparently, ailanthus webworm favors a southern climate. Winters in northern states are just a bit too chilly to support its survival. Like monarch butterflies, milkweed bugs, and fritillary butterflies we met before, the adult stage of ailanthus webworms, magnificent ermine moths, are vagabonds. Each year they migrate from winter redoubts in the south to reach TOH in northern states on which to lay eggs. In a warming world, some experts predict that ailanthus webworm will be able to survive in more northerly states, thereby expanding its range.
Small Tree of Heaven saplings can be shredded and killed by ailanthus webworm caterpillars. These snaky rascals writhe inside their webs. Ah, but the adult stage, a pretty ermine moth, pollinates wildflowers in summer and autumn. Although a bane to grape growers and a nuisance to others, prolonged, high-density infestations of lanternflies drain nutrients from Tree of Heaven. Some like these may be killed by spotted lanternflies, or from lethal teamwork by one native and one non-native herbivore.
Spotted lanternflies often reach huge densities and rob vital nutrients from Tree of Heaven.
In addition to ailanthus webworm, TOH is assaulted by its ancient acquaintance from Asia, the spotted lanternfly. Back in China, spotted lanternflies spent millions of years “learning” how to cope with TOH’s defenses and exploit nutritious phloem sap as a source of food. In late summer and autumn, hundreds, maybe even thousands of spotted lanternfly nymphs and adults can be found draining nutrients from the branches and trunks of TOH. With persistent infestations and vast numbers, lanternflies can be lethal to invasive TOH according to scientists at Penn State.
With young TOH under siege from ailanthus webworm and established TOH assaulted by sap-sucking lanternflies, we might hold hope that these two herbivores may kill some or many TOH and help thwart the ecological impacts of TOH in our natural and managed ecosystems.
Acknowledgements
The interesting articles, “A review of the New World Atteva Walker moths (Yponomeutidae, Attevinae)” by Vitor O. Becker, “Spotted Lanternfly Frequently Asked Questions” by Heather Leach, and “Michigan insects in the garden – Season 2 Week 8: Ermine moths” by David Lowenstein were used as references for this episode.