Adult Season Guide

ADULTS ARESWARMING

PEAK SEASON — AUGUST-OCTOBER

This is the moment. Adults are mating, feeding, and laying egg masses right now. Every adult you kill means 30–50 fewer insects next year. Here's what to do.

1–2

Egg masses per female

30–50

Eggs in each mass

Until frost

Adults active — act now

What You'll See

Adult season has a distinctive look, smell, and feel. You'll know it when it arrives.

You'll know adult season has arrived when you see: clusters of 20–50 gray-tan moths on tree trunks at dusk. They don't fly much during the day. At night they aggregate on Tree of Heaven, grapevines, and other hosts. In the morning, you'll see the honeydew — a shiny, sticky coating on everything below the tree.

What adults look like

—1–1.25" long with wings folded — looks like a gray moth
—Forewings: tan/gray with distinctive black spots arranged in rows
—When disturbed — wings open to reveal BRIGHT RED hindwings with black spots and white band
—Underwings so vivid people often think it's a different species

The swarm at dusk

—Adults are most visible in the 2 hours before sunset
—They walk UPWARD on tree trunks — climb to top, fly to another tree, repeat
—In heavy infestations: dozens visible on a single trunk
—They don't sting, bite, or harm humans

The honeydew

—Shiny, sticky droplets fall from feeding SLF above
—Collects on outdoor furniture, cars, leaves, pavement
—Smell: faintly sweet, slightly fermented as it dries
—Black sooty mold develops within days on the honeydew

The egg-laying

—Females begin laying eggs by late August / early September
—Eggs are laid on any hard surface — not just trees
—After laying: the mass looks like a smear of gray putty ~1" x 0.5"
—One female lays 1–2 masses before dying in fall frost

Your Adult Season Action Plan

Five things to do right now, in order of impact.

SQUISH ON SIGHT

✓During the day, adults are slow and sluggish — easy to catch and kill
✓At dusk, they're active — clap hands around clusters on trunks
✓A wooden board works great: press against trunk cluster
✓Wear gloves if desired (they have no venom, no defense mechanism)

Log your kills →

PROTECT HIGH-VALUE PLANTS

✓Grapevines and hops are at highest risk for economic damage
✓Apply dinotefuran bark spray to ToH at field margins (draws SLF away from vines)
✓Circle traps remain effective through adult season

See control options →

HUNT FOR EGG MASSES (STARTING LATE AUGUST)

✓Females begin laying by late August — scraping masses NOW prevents next year's population
✓Check: fence posts, tree bark, patio furniture, outdoor storage, vehicles, stone walls
✓Each mass you scrape = 30–50 fewer nymphs next spring

Full egg mass guide →

CHECK VEHICLES BEFORE TRAVELING

✓SLF hitchhike on vehicle undercarriages, wheel wells, and bumpers
✓A single egg mass transported from PA to OH creates a new population
✓Check your car if you've been in a heavily infested area before driving long distances

REPORT EVERY SIGHTING

✓Your reports trigger researcher attention and intervention
✓Especially valuable: first reports in a new county or ZIP code

Report a sighting →

The Egg Mass Window

The window to interrupt next year's infestation opens in August and closes in April. Act now.

Late August

Window Opens

First egg masses appear. Females have been feeding for weeks and begin laying.

September

Peak Laying

Peak egg-laying month. Every day counts — each mass left means 30–50 more nymphs next spring.

October

Still Laying

Last females still active and laying before frosts arrive. Adults beginning to die off.

November

Adults Gone

Adults dead after first hard frost. Only egg masses remain — fully viable all winter.

April–May

Hatch Begins

Eggs hatch into black nymphs. Next year's infestation begins from every mass left unchecked.

The compounding effect: Every adult you kill now prevents 30–50 eggs. Every egg mass you scrape before April prevents 30–50 nymphs. Act in August and September — before next year's infestation is locked in.

Egg Mass Prevention Guide →