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Barnacle scale

Ceroplastes cirripediformis[3]

Barnacle scale is a soft scale insect that hides under a thick, pearly-gray cap of wax on the stems of gardenias, citrus and many other plants; heavy infestations drip honeydew that grows black sooty mold.[1][2]

Group
Insect
Order
Hemiptera
Family
Coccidae
US records
14 states
Sources
3 cited
Updated
2026-10-19
Barnacle scale on a twig, a rounded, pearly-gray wax-covered scale with plates outlined by shallow grooves
Barnacle scale on a twig, a rounded, pearly-gray wax-covered scale with plates outlined by shallow grooves. (c) RAP, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Where it lives
  3. Biology
  4. Damage and signs
  5. Health risk
  6. Control
  7. Related profiles
  8. Common questions
  9. Sources

How to identify it

  • Mature females are about 1/4 inch long, rounded and covered in thick, pearly-gray wax divided by shallow grooves into plates, each with a darker spot around a small wax button; the large rear plate has three buttons.[1][2]
  • Nymphs are reddish and partly covered with pure white, star-shaped or conical wax plates; they feed on top of leaf veins before moving to the stems.[1][2]

Where it lives

It is a landscape pest from the Southeast, where gardenia is its most common host in North Carolina, to southern California, where it is mainly a pest of gardenia.[1][2]

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

Biology and life cycle

Adults are present on stems and twigs from late July through winter; each female lays hundreds of eggs under her wax.[1][2]

Crawlers probably emerge in late May to early June and settle on the tops of leaves, then move to stems after their second molt; there is one generation a year.[1][2]

It has been recorded on citrus, gardenia, guava, passion flower and plants in 119 genera and 63 families.[1]

Damage and signs

  • Barnacle scales suck plant sap and excrete large amounts of honeydew, leaving a gooey mess and black sooty mold on leaves and objects below.[2][1]

Health risk

It feeds only on plants; NC State and UC IPM mention no risk to people.[1][2]

Control

Biological control

Control ants on infested plants, since ants attack the natural enemies of scale insects.[2]

Pesticides

Time any spray for when crawlers are out on the tops of leaves in late May to early June; once settled under wax, scales are hard to reach. NC State notes related wax scale crawlers are highly susceptible to carbaryl (Sevin) and pyrethroid sprays.[1]

Common questions

What are the gray, waxy bumps on my gardenia stems?
Likely barnacle scales, soft scale insects under a thick, pearly-gray wax cover; gardenia is their most common host in North Carolina.[1]
When should I spray for barnacle scale?
When the crawlers hatch and move onto the leaves, around late May to early June; sprays do little once the scales are settled under their wax.[1]

Sources

  1. NC State Extension, “Barnacle Scale.” content.ces.ncsu.edu/barnacle-scale (accessed 2026-10-19)
  2. University of California Statewide IPM Program, “Wax scales (Home and Landscape).” ipm.ucanr.edu/home-and-landscape/wax-scales/ (accessed 2026-10-19)
  3. iNaturalist, “Ceroplastes cirripediformis taxon page (order and family).” www.inaturalist.org/taxa/120449 (accessed 2026-10-06)

Updated 2026-10-19. Built from sourced records. Spot an error? Tell us.