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Woolly Elm Aphid

Eriosoma americanum[3]

The woolly elm aphid is an aphid that curls elm leaves in spring and spends the summer on serviceberry roots.[1][2]

Group
Insect
Order
Hemiptera
Family
Aphididae
US records
27 states
Sources
3 cited
Updated
2026-10-17
Elm leaf rolled under along its edge by woolly elm aphids
Elm leaf rolled under along its edge by woolly elm aphids. (c) Emily Summerbell, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Related profiles
  9. Common questions
  10. Sources

How to identify it

  • The aphids are tiny, about 0.08 inch long, and dusted with light gray wax.[2]
  • Infested elm leaves roll under from the edge toward the midrib, often turning reddish or brown, and fill with aphids and shed skins.[1][2]
  • By late June the crowded leaf rolls overflow with aphids.[1]

Look-alikes

Look-alikeHow to tell them apart
Woolly apple aphidA related Eriosoma aphid that also uses elm but spends the summer on apple, forming white woolly patches and galls on bark and roots.[2]

Where it lives

Found on American elm in New England and on elms in the Pacific Northwest.[1][2]

US map: public records from 27 states since 1990 (GBIF).

Biology and life cycle

Eggs overwinter in elm bark crevices and hatch as leaves unfold; one wingless female can produce about 200 young without mating.[1][2]

Winged aphids leave the curled leaves for serviceberry, feed on its roots for several generations through summer, then fly back to elm in fall to lay eggs.[1][2]

Damage and signs

  • On elm the damage is mostly cosmetic, though heavy infestations can weaken small trees.[1][2]
  • Root feeding can badly damage serviceberry seedlings; UMass cites a study where up to 85 percent of saskatoon berry seedlings were lost.[1]

Health risk

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

Control

Prevention

Avoid planting elm near serviceberry, although the winged aphids can travel long distances.[1]

Traps and physical control

On small trees, pick off and destroy curled leaves with aphids early in the season.[1]

Biological control

Lady beetles, lacewings, hover fly larvae and the parasitoid wasp Aphelinus mali attack it, and predators are often already at work when the aphids are noticed.[1][2]

Pesticides

Check trees as they leaf out; once leaves are curled the damage can't be undone, so any treatment has to come early.[2]

Common questions

Why are my elm's leaves curled and full of white fluff?
Woolly elm aphids feeding inside the curled leaves are a common cause.[1][2]
Do woolly elm aphids hurt serviceberry?
They feed on serviceberry roots in summer and can seriously damage seedlings.[1]

Sources

  1. UMass Extension Landscape, Nursery and Urban Forestry Program (Landscape Insect & Mite Guide), “Eriosoma americanum (Woolly Elm Aphid).” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/eriosoma-americanum (accessed 2026-10-16)
  2. Pacific Northwest Insect Management Handbook (Oregon State, Washington State, University of Idaho), “Elm (Ulmus)-Aphid (Hosts and Pests of Landscape Plants).” pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/elm-ulmus-aphid (accessed 2026-10-16)
  3. iNaturalist, “Eriosoma americanum taxon page (order and family).” www.inaturalist.org/taxa/454393 (accessed 2026-10-06)

Updated 2026-10-17. Built from sourced records. Spot an error? Tell us.