Hackberry trees sometimes host hackberry gnats, tiny insects that become noticeable in late summer and fall. While annoying, these gnats are generally harmless to trees and people. They do not bite or transmit diseases, but their sheer numbers can be bothersome as they seek refuge indoors.
Identifying Hackberry Gnats and Their Origin
Hackberry gnats are actually hackberry psyllids, also known as hackberry nipple gall makers or jumping plant lice. These small, winged insects measure about 2.5–5 mm long. They have mottled brown bodies and clear-banded wings held roof-like over their backs, resembling miniature cicadas. Their enlarged hind legs allow them to jump when disturbed, earning them the “jumping plant lice” nickname.
The life cycle of hackberry psyllids is tied to hackberry trees. Adults lay eggs on new leaves in early spring. The hatching nymphs feed on the leaves, stimulating the formation of distinctive “nipple galls” on the leaf surfaces. These galls protect the psyllid nymphs as they develop throughout the summer. Adult psyllids emerge from these galls in late summer or fall, typically from late August through October, leading to their noticeable swarming behavior.
Impact on Trees and People
Hackberry psyllids and their galls are primarily a cosmetic issue for hackberry trees. While unsightly, they rarely cause significant harm to the overall health of mature trees. Severe infestations might lead to some leaf distortion or premature leaf drop, but healthy, established trees tolerate their presence without lasting damage.
For humans, hackberry gnats pose no direct threat. They do not bite, sting, or transmit diseases to people or pets. Their main impact is as a nuisance due to their large numbers, especially during fall. They are attracted to light-colored surfaces and lights, often congregating on homes and finding their way indoors through small gaps or standard window screens.
Effective Management Strategies
Outdoor chemical treatments for hackberry psyllids are generally not practical or recommended for homeowners. Applying insecticides to large trees is difficult and requires multiple applications in early spring when eggs hatch. Adults can also re-infest from surrounding trees, making local treatments ineffective for long-term control. Additionally, galls protect developing nymphs, limiting spray effectiveness once formed.
The most effective approach focuses on preventing hackberry psyllids from entering homes. Inspect and repair any tears or gaps in window screens, as their small size allows them to slip through. Seal cracks around windows and doors, and ensure weather stripping is intact to block entry points. Turning off outdoor lights at night or switching to yellow, non-insect-attracting bulbs can also reduce their attraction.
If hackberry psyllids get inside, vacuuming is the most effective removal method. Promptly seal and dispose of vacuum bags or empty canisters, as the insects can survive inside. Cleaning up fallen hackberry leaves in the fall, which contain galls, may help reduce overwintering populations, though this has limited impact regionally. For exterior clusters on siding, hosing them off with water can provide temporary relief.
Prevention and Nuisance Mitigation
For new plantings, consider selecting hackberry varieties that show some resistance to gall formation. While not a solution for existing trees, this offers a proactive choice for future landscaping.
Promoting the overall health of existing hackberry trees through proper watering and mulching can help them better withstand pest pressures, though it does not prevent gall formation entirely. Awareness of the psyllids’ peak emergence season in late summer and fall allows homeowners to take proactive exclusion measures before swarms begin.
Ultimately, managing hackberry gnats is about mitigating their nuisance rather than aiming for complete eradication. Since they are harmless to trees and pose no health risk to people, patience and consistent exclusion efforts are key. Populations naturally decline as the season progresses and temperatures drop.