Spotted lanternflies pierce ash bark in summer

The air holds thick and still above the Potomac's edge, where the long days of summer stretch into evening. Heat radiates from the pavement and settles into the canopy of white ash and American elm that line these urban streets. If you are walking here, let the sounds of the city fade for a moment. The trees themselves are busy with smaller, quieter dramas.

On the bark of a white ash, a cluster of spotted lanternflies feeds. These invasive insects arrived from Asia and have spread rapidly across the mid-Atlantic. The nymphs are black with white spots, about the size of a thumbnail, and they pierce the bark with needle-like mouthparts to reach the tree's phloem. The phloem carries sugar-rich sap from the leaves down to the roots. The lanternflies tap directly into this flow, drawing out the nutrients the tree needs to sustain itself through the growing season.

The feeding happens in groups. Where you find one spotted lanternfly, you find dozens. They cluster on the same section of bark, their bodies pressed close together as they probe for the sweetest channels of sap. The ash tree responds by producing more sap to seal the wounds, but this only attracts more lanternflies. The excess sap they cannot process drips down the trunk as honeydew, a sticky substance that coats the bark and feeds sooty mold. The tree's trunk darkens with this black fungus, and the ground below becomes slick with the sugary residue. American elms face the same assault. Their smooth bark shows the telltale weeping where lanternflies have concentrated their feeding. The elms, already stressed by Dutch elm disease and urban conditions, struggle under this additional pressure. A heavily infested tree may lose significant amounts of sap, weakening its ability to transport nutrients and defend against other threats. The honeydew that accumulates on leaves blocks sunlight, reducing photosynthesis when the tree most needs energy to repair the damage.

Native insects that might normally feed on these trees find their feeding sites occupied. The spotted lanternflies do not belong to the web of predator and prey relationships that have developed here over thousands of years. Few native birds recognize them as food. Few native parasites can control their numbers. They feed without the natural checks that keep native plant-feeders in balance with their host trees. As the afternoon heat builds, you might notice the sweet, cloying smell of fermenting honeydew rising from an infested tree. The bark feels tacky to the touch where the excess sap has dried. Listen closely, and you can hear the faint sound of dripping as more sap weeps from fresh feeding wounds.