A COLORFUL NUISANCE: The spotted lanternfly is back in Princeton for a fourth summer. It appears as a small black insect in its early stages of growth, but by midsummer the adult lanternflies will be flying around in full color, leaving their sticky black excretions on tree trunks, cars, patios, and walkways. Tree experts recommend that residents remove the lanternfly’s host tree, the ailanthus or tree of heaven.

By Donald Gilpin

“They have hatched!” The text message from the Princeton municipal arborist arrived at 8:30 a.m. on Monday. “Just saw them today.” Beginning as a harmless-looking little black insect or nymph, the spotted lanternfly (Lycorma delicatula) will grow into the colorful flying adult insect that drops from trees, lands everywhere, and excretes a sticky black substance onto patios, sidewalks, cars, and trees.

“You’ll see the nymphs, the little black insect,” said Princeton Municipal Arborist Taylor Sapudar. “Then they’ll develop into the second phase, a little red crawler, but we won’t be seeing the adults — the ones that are flying around and landing on you — until midsummer.”

He continued, “So far it does not appear to be an insect that will cause major hardwood damage to the tree. A lot of residents are under the impression that it’s going to act similarly to the emerald ash borer, which completely kills the ash tree, but the spotted lanternfly is more of a cosmetic or ornamental nuisance.”

Sapudar described what many Princeton residents can expect two or three months from now. “They may be on trees overhanging your driveway or your patio,” he said. “When they feed they’re going to excrete that black sticky substance that has the potential to get onto your car or elsewhere.”

He went on to outline a strategy of destroying the spotted lanternfly’s preferred habitat, the tree of heaven or ailanthus tree. He noted, however, “if they’re on an ornamental tree like a maple or birch, to remove the tree is not recommended at all.”

Princeton residents, he said, should follow the example of the municipality and remove ailanthus trees. “When ailanthus trees are within the right of way we remove them and we stump grind them,” he said. “They should be stump ground because otherwise they will come back with vengeance to regrow. Consult with your contractor on getting those residual roots and getting that stump out of there. The whole tree should be eliminated or else they’re going to have a residual problem.”

Sapudar explained that the municipality usually removes all the female ailanthus trees, the ones with seed heads, and leaves just one or two male trees to use in trapping spotted lanternflies so they don’t move on to other ornamental trees. The spotted lanternflies will be confined to the one or two male trees, rather than dispersing widely, and they can be more easily destroyed.

The ailanthus is an invasive tree often found on the edge of woods, the back of parking lots, edges of roads, and other areas that are not mowed regularly.

The spotted lanternfly is not dangerous to humans or animals, but it does reduce plant vigor and it can pose a threat to agriculture, especially fruit trees and the grape vine. In addition to trapping, tree care professionals can also administer organic and synthetic insecticides, depending on the management plan that best suits each individual situation.

The spotted lanternfly is a plant hopper native to China. It first appeared in the United States when it was accidentally introduced into Pennsylvania in 2014. It was first seen in New Jersey in 2018 and in Princeton in 2019. It is now also in parts of Connecticut, Delaware, Indiana, Maryland, Massachusetts, New York, Ohio, Virginia, and West Virginia.

The spotted lanternfly feeds on plants using its sucking and piercing mouth parts to extract plant sap. It excretes large quantities of a liquid sap, also called honeydew, that facilitates the growth of sooty mold. The sap also attracts wasps, hornets, ants, and bees.

The spotted lanternfly life cycle is one year. Egg masses, which can contain up to 50 eggs, are laid in the fall and hatched in the spring of the following year. If egg masses are seen, it is recommended that they be scraped and removed.

Though the future of the spotted lanternfly and its residence in Princeton remain uncertain, Sapudar voiced a hint of optimism. Last year he talked with foresters and public works directors in the Berks County, Pa., area where the spotted lanternfly was first observed in 2014.

“They saw a peak in spotted lanternfly numbers in the fifth, sixth, and seventh years and a decline in spotted lanternflies over the past two years,” said Sapudar. “They suspect that’s because people are removing ailanthus trees, the tree of heaven, which is the spotted lanternfly’s primary host. They had increased populations and now they’re seeing decreased populations, so I’m optimistic that the same will occur here.”

For further information, visit the New Jersey Department of Agriculture at nj.gov, the U.S. Department of Agriculture at aphis.usda.gov, and the New Jersey Board of Tree Experts and njtreeexperts.org.