The non-native, misleadingly named Tree-of-Heaven (Ailanthus altissima, family Simaroubaceae) is the primary host for Spotted Lanternfly (SLF) (Lycorma delicatula). This should not be surprising given that the tree and planthopper “grew up together” in Asia.
The magnetic attraction of tree-of-heaven to SLF makes the invasive tree a highly effective sentinel for detecting the invasive planthopper in Ohio. Of course, the SLF investigative light shining on tree-of-heaven may also expose web-nesting webworms.
I recently came across heavy infestations of so-called Ailanthus Webworms (Atteva aurea) while searching for SLF on tree-of-heaven in southwest Ohio. The webworms are the larval (caterpillar) stage of a beautiful ermine moth (Family Yponomeutidae), and they feed exclusively on tree-of-heaven.
The moths curl their wings lengthwise along their bodies giving them a tubular shape. This coupled with commonly being found on a wide range of flowers located far from their childhood homes on their namesake host can present an ID challenge.
Multiple overlapping generations occur each season, so it’s common to find moths and caterpillars active at the same time. Both are active throughout the season with the moths appearing on early and late-blooming plants.
The webworms produce communal nests by pulling leaflets into a network of loose webbing. Several caterpillars live within the nests consuming the leaflets enveloped in their webbing. It’s common to find mixed-aged caterpillars inhabiting the same nests owing to overlapping generations.
The webworms can grow up to 1 - 1 1/2" long and they have a wide, light brown to greenish-brown stripe down their backs and several thin, alternating white and olive-green stripes along their sides. The caterpillars are sparsely covered with short, erect hairs, which help to suspend them within the webbing. When disturbed, the caterpillars move backward out of the nest and drop on strands of silk towards the ground.
Ailanthus webworm caterpillars are capable of defoliating their odoriferous namesake host and they may feed on stem tissue once all of the leaves are devoured. I’ve seen entire understory “colonies” of tree-of-heaven seriously damaged by the caterpillars.
Unfortunately, such extreme damage is rare on large trees, and lost sprouts are replaced by their relatives springing forth from underground rhizomes. Of course, new trees may also arise from bumper crops of seeds produced by tree-of-heaven female trees. Sadly, feeding by the webworm has yet to halt the invasive spread of tree-of-heaven; however, hope springs eternal.
All in the Family
The host preference of SLF is easy to understand given it co-evolved with tree-of-heaven in Asia. However, the Ailanthus webworm’s exclusive preference for the non-native tree-of-heaven may be more difficult to understand since the moth is a "New World" insect native to southern Florida and as far south as Costa Rica.
In its native range, A. aurea caterpillars originally fed on two members of the family Simaroubaceae, the paradise tree (Simarouba glauca) and S. amara. However, when tree-of-heaven which also belongs to the same plant family was introduced and naturalized in the native range of A. aurea, the caterpillars found the non-native interloper to their liking and jumped ship to exploit a new resource.
Of course, the moths expanded their range along with the ever-expanding range of tree-of-heaven to move north in the U.S. and into Canada. Its strong preference for tree-of-heaven gave rise to the common name, “Ailanthus webworm,” although this name has not yet been approved by the Entomological Society of America as the common name for A. aurea.
Help Us Spot the Spotted
Tree-of-heaven remains a focal point for detecting new SLF infestations. Ailanthus webworm is interesting; however, it’s mostly an oddity and takes a back seat to SLF regarding potential ecological and agricultural impact.
Please help us spot SLF in Ohio by giving tree-of-heaven close looks. The lanternfly has completed its development through four nymphal instar stages and is now in the adult stage in Ohio. The adults are one of the largest planthoppers you’d ever come across. However, their general appearance may cause some people to mistake them for moths. On the other hand, SLFs garish coloration is unique and easy to spot particularly when the adults "flash" their deep red hind wings.
If you spot SLF, please take the following steps:
1. Take a digital picture.
2. Bag the specimen(s) and keep them cool (frozen is OK) until arrangements can be made with the Ohio Department of Agriculture (ODA) for them to acquire the specimen(s). SLF isn’t “confirmed” in a new county until a specimen is examined by the ODA along with the USDA Animal and Plant Health Inspection Service (APHIS).
3. Click the hotlink below to report your find to the ODA. The brand new easy-to-use website was launched last week and allows you to upload your picture(s) and to use an interactive map to mark the exact location:
https://agri.ohio.gov/divisions/plant-health/invasive-pests/slf