Pest profile

Kermes Scales

Kermesidae (e.g., Allokermes and Nanokermes species) · Hemiptera: Kermesidae[3]

Kermes scales are round, smooth scale insects on oak twigs and leaves that look like buds or small galls; heavy infestations deform and stunt new growth.[1][2]

Cluster of round, beige kermes scales on an oak twig
Cluster of round, beige kermes scales on an oak twig. (c) Cricket Raspet, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Mature females are smooth and globular, about 1/8 to 1/4 inch across, creamy white to beige, brown or nearly black depending on species.[1][2]
  • Unlike real buds or galls, they pop off the twig easily.[1]

Where it lives

About nine species in four genera occur in the Northeast and at least 32 in North America; in Iowa, the one on bur oak causes the most damage.[1][2]

US map: public records from 14 states since 1990 (GBIF).

Biology and life cycle

Crawlers spend the winter in bark cracks, migrate to new twigs in spring and settle to feed on sap.[1][2]

For the best-studied species, females lay eggs over about a month starting in late June, and eggs hatch in early July.[2]

Damage and signs

  • Large numbers on new branches and leaves cause deformed, stunted growth.[1]

Health risk

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

Control

Biological control

Predators and parasites help keep populations in check.[1]

Pesticides

If scales are a problem several years in a row, use a product labeled for kermes or soft scales: dormant oil before leaf-out, contact insecticides when crawlers are active in spring, or a systemic.[1]

Common questions

What are the round brown bumps on my oak twigs?
Possibly kermes scales; unlike buds or galls they come off the twig easily.[1]
Do kermes scales hurt oaks?
Heavy infestations deform and stunt new growth, especially on bur oak in Iowa.[1]
When should kermes scale be treated?
Only if it persists several years: dormant oil before leaf-out or contact sprays when spring crawlers are active.[1]

Sources

  1. Iowa State University Extension and Outreach (Yard and Garden), “Kermes Scale.” yardandgarden.extension.iastate.edu/encyclopedia/kermes-scale (accessed 2026-10-15)
  2. UMass Extension Landscape, Nursery and Urban Forestry Program (Landscape Insect & Mite Guide), “Allokermes spp. (Kermes Oak Scale).” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/allokermes-spp (accessed 2026-10-15)
  3. iNaturalist, “Allokermes taxon page (order and family).” www.inaturalist.org/taxa/49029 (accessed 2026-10-06)

Updated 2026-10-15. Built from sourced records. Spot an error? Tell us.