Giant Bark Aphid

How to identify it

• Aphids are about 1/4 inch long with long legs, light gray to grayish black, with four rows of black spots down the back.^[1][2]
• They cluster on the bark of one- to three-year-old stems rather than on leaves, and leave an iodine-colored stain when crushed.^[2]
• Winged adults have translucent gray wings.^[1]

Where it lives

NC State and Iowa State both report it; populations peak and are most noticed in late summer.^[1][2]

US map: public records from 31 states since 1990 (GBIF). View the map

Biology and life cycle

During the growing season females give birth to females without mating, so numbers can rise quickly.^[1]

In fall, males and egg-laying females appear, and the eggs overwinter on twigs, turning shiny black.^[1]

They insert their mouthparts through the bark into the sap-carrying tissue and excrete the excess sugar as honeydew.^[1][2]

Damage and signs

• Hosts include basswood, birch, elm, hickory, maple, oak, pecan, sycamore, walnut, wax myrtle and willow.^[1][2]
• Heavy honeydew grows sooty mold that can blacken plants; heavy infestations may cause stunting or twig dieback, though healthy trees often tolerate large populations.^[1][2]
• Aphids may wander from infested trees onto sidewalks, decks and patios.^[2]

Health risk

None to people or pets.^[1][2]

Control

Biological control

Parasitic wasps, lady beetles, syrphid fly maggots, lacewings and an aphid-killing fungus often reduce populations rapidly.^[1]

Pesticides

Control in late summer or fall is usually not warranted; treat early-summer populations on young or stressed plants, and horticultural oils work well.^[1][2]

Common questions

What are the big gray bugs clustered on my tree branches?

In late summer they are often giant bark aphids, the largest aphid, feeding through the bark.^[1][2]

Why is everything under my tree sticky and black?

Honeydew from the aphids, with sooty mold growing on it.^[1]

Should I spray giant bark aphids?

Usually not in late summer or fall; natural enemies often knock them back quickly.^[1][2]

Sources

1. NC State Extension, “Giant Bark Aphid (PDIC Factsheet).” content.ces.ncsu.edu/giant-bark-aphid (accessed 2026-10-15)
2. Iowa State University Extension and Outreach (Yard and Garden), “Giant Bark Aphid.” yardandgarden.extension.iastate.edu/encyclopedia/giant-bark-aphid (accessed 2026-10-15)
3. iNaturalist, “Longistigma caryae taxon page (order and family).” www.inaturalist.org/taxa/332640 (accessed 2026-10-06)