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How to identify it
- Adult female elongate-oval, shiny and dark brown, 3 to 4 mm long; at maturity the back is strongly hardened and marked with a network of polygons, each with a minute pore at its center.[1]
- Shape depends on where it settles: scales on leaves are broad and only slightly convex, while those on stems or leaf midribs are elongate and much more convex.[1]
- Immature stages and young adults are translucent yellow and sometimes mottled, so a colony shows pale young scales beside dark mature females.[1]
- A soft scale (family Coccidae): the cover is the insect's own body wall and cannot be lifted off, and the insect excretes sticky honeydew on which blackish sooty mold grows.[3]
- Found on an unusually wide range of hosts, more than 80 plant families by one count and 101 in ScaleNet, including hibiscus, Ficus elastica and F. religiosa, oleander, avocado, mango, schefflera and ixora.[1][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Black scale (Saissetia oleae) | The soft scale UC IPM calls black scale; nigra scale shares the 'black scale' name in some catalogues but belongs to a different genus and is described as a shiny, elongate-oval, dark brown insect 3 to 4 mm long.[1][3] |
| Brown soft scale | Another common soft scale on indoor and landscape plants; UC IPM notes it has multiple generations with females and nymphs present year-round, whereas most soft scales have one generation a year.[3] |
| Other soft scales | UC IPM's soft scales grow up to 1/4 inch with a smooth, cottony or waxy surface and a cover that is the body wall itself; nigra scale is the shiny dark brown one whose shape changes with the plant part it settles on.[3][1] |
Where it lives
ScaleNet records nigra scale in the United States from Alabama, California, Florida, Kansas, Louisiana, Maryland, Missouri, New Mexico, New York, Ohio, Oklahoma, Pennsylvania, Texas, Virginia and Washington, as well as Hawaii; Lin and colleagues describe it as a cosmopolitan pest.[1][2]
Biology and life cycle
Nigra scale is parthenogenetic, reproducing without males, cosmopolitan and polyphagous, feeding on plants from more than 80 families.[2]
Its life history, ecology and natural enemies were studied in California by Smith in 1944. In the laboratory it develops on squashes and sprouting potato tubers; on squash at 24 C (75 F) a generation takes 45 to 60 days. In Tamaulipas, Mexico, at least two complete generations a year were observed on mistletoe.[1]
Genetic analyses of mitochondrial and nuclear genes plus ecological niche modelling indicate that what is called P. nigra comprises at least two ecotypes that differ particularly in the temperatures and moisture they tolerate; some countries may hold only one, so introducing another lineage could expand the pest's range.[2]
Like other soft scales it feeds on phloem sap and excretes abundant honeydew. Natural enemies recorded on it include Metaphycus and Coccophagus parasitic wasps.[3][1]
Damage and signs
- ScaleNet rates it a potential pest of litchi in Israel; its damage elsewhere is that of a honeydew-producing soft scale on ornamentals and fruit trees. Scales in large numbers can weaken a plant, slow its growth, yellow the leaves and cause premature leaf drop and dieback, and the honeydew, sooty mold and ants it attracts can be a nuisance even when the plant itself is not harmed.[1][3]
Health risk
A plant-feeding scale insect; neither the catalogue nor UC IPM reports any risk to people or pets.[1][3]
Control
Sanitation
Inspect trunks for ants during the growing season and control honeydew-seeking ants, which protect scales from their natural enemies.[3]
Traps and physical control
Wrap double-sided sticky tape around infested twigs in spring and change it weekly to catch crawlers; spray only after crawler numbers on the tape have peaked and begun to decline.[3]
Biological control
Many scales are well controlled by predators and parasitic wasps unless those natural enemies are disrupted by ants, dust or persistent broad-spectrum insecticides. Nigra scale's recorded enemies include Metaphycus and Coccophagus wasps; before spraying, check a sample of scales to see whether they are already dead or parasitized.[3][1]
Pesticides
A well-timed, thorough spray of horticultural (narrow-range) oil in the dormant season or soon after crawlers are active gives good control of most scales. Insecticidal soap, neem oil and other botanical oils are low-toxicity contact alternatives that need complete coverage of shoot terminals and leaf undersides, and may need repeating where the scale has more than one generation a year.[3]
On large plants or hosts especially sensitive to scale damage a systemic insecticide may be warranted; if a plant is repeatedly damaged, UC IPM suggests replacing it with a species or cultivar better suited to the site.[3]
Common questions
- How is nigra scale different from the black scale on my olive and citrus?
- Black scale (Saissetia oleae) is a different genus. Nigra scale is an elongate-oval, shiny dark brown soft scale 3 to 4 mm long that is flat on leaves and humped on stems; some catalogues also call it black scale, hibiscus scale or pomegranate scale, which causes the confusion.[1][3]
- Why does the same scale look flat on leaves and humped on stems?
- ScaleNet notes the body shape varies with the substrate: specimens on leaves are broad and only slightly convex, while those on stems or leaf midribs are elongate and much more convex.[1]
- Is one spray enough?
- Horticultural oil timed to the dormant season or to crawler activity controls most scales, but contact sprays need thorough coverage and may need repeating when a scale has more than one generation a year; in warm conditions nigra scale completed a generation in 45 to 60 days in laboratory tests.[3][1]
Sources
- ScaleNet (scale insect database begun at the USDA ARS Systematic Entomology Laboratory), “ScaleNet catalogue: Parasaissetia nigra (Nietner, 1861).” scalenet.info/catalogue/Parasaissetia%20nigra/ (accessed 2026-11-10)
- PLoS One, abstract via PubMed, “Species delimitation in asexual insects of economic importance: the case of black scale (Parasaissetia nigra), a cosmopolitan parthenogenetic pest scale insect (Lin et al. 2017, PLoS One 12(4):e0175889; PubMed 28459805).” doi.org/10.1371/journal.pone.0175889 (accessed 2026-11-10)
- University of California Statewide IPM Program, “Pest Notes: Scales (UC ANR Publication 7408).” ipm.ucanr.edu/home-and-landscape/scales/ (accessed 2026-11-10)
- iNaturalist, “Parasaissetia nigra taxon page (order and family).” www.inaturalist.org/taxa/330206 (accessed 2026-11-10)