Scale Insects Identification Guide
Coccoidea
Scale insects are small sap-feeding pests that attach to plant stems, leaves, and bark. They appear as small bumps or waxy growths and can cause yellowing, wilting, and branch dieback in ornamental plants, houseplants, and landscape trees.
Taxonomy
Scale Insects Coloration
Common color patterns to help identify scale insects
Scale Insects
Seasonal Activity
When scale insects are most active throughout the year
Where Scale Insects Are Found
Hover over states to see their names. Green regions indicate where scale insects have been reported.
Scale Insects Identification Guide
Physical Characteristics
Scale insects look very different from most pests. Adult females appear as small, still bumps on plant stems and leaves. They range from 1 to 6 millimeters in size. Their shape can be round, oval, or oyster-like.
There are two main types of scale insects. Soft scales have a waxy or cottony coating that is part of their body. Armored scales have a hard, shell-like cover that can be lifted off. Both types come in brown, tan, white, gray, and cream colors.
Adult females have no visible legs. Once they start feeding, they stay in one spot. Male scale insects are rarely seen. They are tiny, winged insects that look like small flies. Males live only long enough to mate.
Common Species in North America
Soft Scales:
- Cottony cushion scale (Icerya purchasi): makes white, cottony egg masses
- Brown soft scale (Coccus hesperidum): common on houseplants and citrus
- Magnolia scale (Neolecanium cornuparvum): one of the largest soft scales, found on magnolia trees
- Cottony maple scale (Pulvinaria innumerabilis): affects maples and other shade trees
- Oak lecanium scale (Parthenolecanium quercifex): found on oaks and other hardwoods
Armored Scales:
- San Jose scale (Quadraspidiotus perniciosus): serious pest of fruit trees
- Euonymus scale (Unaspis euonymi): attacks euonymus and pachysandra
- Oystershell scale (Lepidosaphes ulmi): common on shade trees and shrubs
- Tea scale (Fiorinia theae): affects camellias and hollies
- Pine needle scale (Chionaspis pinifoliae): found on pines and other evergreens
Scale Insects Behavior and Biology
Lifecycle
Scale insects have different life stages for males and females. Females go through egg, crawler, and adult stages. Males have more stages, including a pupal stage before becoming adults.
Most scale insects spend winter as eggs under the dead female’s shell. Some spend winter as young scales on twigs and branches. In spring, tiny crawlers hatch and move across the plant to find a feeding spot. The crawler stage lasts a few days to a few weeks.
When crawlers find a good spot, they push their needle-like mouths into the plant and start feeding on sap. Soft scales may move a bit as they grow. Armored scales stay in one place for life. After settling, the insect starts making its protective shell.
Feeding Habits
Scale insects feed only on plant sap. They use their straw-like mouths to pierce plant tissue. Soft scales produce honeydew, a sticky sweet liquid that attracts ants. This honeydew can also cause black sooty mold to grow on leaves. Armored scales do not make honeydew.
Heavy infestations weaken plants by draining nutrients and water. Signs of damage include yellow leaves, early leaf drop, slow growth, dying branches, and sometimes plant death. Scale insects often attack plants already stressed by drought or poor care.
Natural Enemies
Several predators help keep scale numbers down. Lady beetles and their larvae eat scale crawlers and adults. Parasitic wasps lay eggs inside scale insects. Lacewing larvae and predatory mites also feed on scales.
Treatment Methods for Scale Insects
Scale insects are hard to control because their shells protect them from many sprays. The best approach uses several methods timed to hit them when they are most exposed.
Cultural Control
- Pruning: Cut off branches with heavy scale infestations. This removes many scales at once and stops spread to healthy branches.
- Plant selection: Choose plants that resist scale problems. Avoid planting too many of the same type in one area.
- Plant care: Keep plants healthy with proper watering and feeding. Healthy plants handle scale damage better and are less likely to attract scales.
Mechanical Control
For small problems, especially on houseplants, you can remove scales by hand. Scrape them off with a soft brush, your fingernail, or a cotton swab dipped in rubbing alcohol. Spray plants with a strong water stream to knock off crawlers. Check plants often and act early before small problems get worse.
Horticultural Oils
Horticultural oils kill scales by coating and suffocating them. Dormant oil sprays in late winter work well on overwintering scales before plants start growing. Lighter summer oils can be used during the growing season when crawlers are active. Avoid spraying during very hot weather to prevent plant damage.
Insecticidal Soaps
Insecticidal soaps are contact sprays that work well against soft-bodied crawlers. They leave no toxic residue once dry. You may need to apply them more than once because soaps only kill insects that get sprayed directly.
Systemic Insecticides
For landscape plants with bad infestations, systemic insecticides can provide season-long control. These products are applied to the soil or injected into the trunk. The plant takes up the active ingredient and moves it through its tissues. Scale insects die when they feed on the treated plant. Systemics work best against soft scales.
Biological Control
Lady beetles and parasitic wasps eat scale insects. In greenhouse settings, these predators can be released to help control scale populations. For home landscapes, targeted treatments work better than broad sprays at keeping scale numbers low over time.
References
Other Garden Pests
Explore other species in the garden pests family
Commonly Confused With
Scale Insects are often mistaken for these similar pests
Where Scale Insects Are Found
Hover over states to see their names. Green regions indicate where scale insects have been reported.
Common Questions about Scale Insects
What are scale insects?
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Scale insects are small, sap-feeding pests that attach themselves to plant stems, leaves, and bark. Adult females are typically immobile and covered by a protective waxy or shell-like covering, which makes them look like small bumps on plants rather than insects.
How do I know if my plants have scale insects?
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Look for small, raised bumps on stems and leaves that can be brown, white, tan, or gray. Other signs include yellowing leaves, sticky honeydew residue on leaves or nearby surfaces, black sooty mold, and overall plant decline or stunted growth.
Are scale insects harmful to humans?
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No, scale insects do not bite, sting, or pose any direct health risk to humans or pets. They are strictly plant pests. However, heavy infestations can kill ornamental plants, houseplants, and landscape trees if left untreated.
What is the sticky substance on my plant?
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The sticky substance is called honeydew, a sugary excretion produced by soft scale insects as they feed on plant sap. Honeydew often attracts ants and can lead to the growth of black sooty mold on leaves and surrounding surfaces.
Can scale insects spread to other plants?
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Yes, scale insects can spread to nearby plants. The mobile crawler stage moves from plant to plant, and crawlers can also be transported by wind, birds, contaminated tools, or when infested plants are moved close to healthy ones.
When are scale insects most active?
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Scale insects are most active during warm months from late spring through early fall. Crawler emergence typically occurs in late spring to early summer, which is the best time for treatment since crawlers are the most vulnerable life stage.
How do I get rid of scale insects on houseplants?
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For light infestations, physically remove scales by scraping them off with a soft brush or cotton swab dipped in rubbing alcohol. For heavier infestations, horticultural oils or insecticidal soaps applied during crawler emergence can be effective. Severely infested plants may need to be discarded to protect other plants.
With five years of hands-on experience in the pest control industry, George Schulz is a registered technician with the Virginia Pest Management Association and a proud third-generation professional in a family business that's been protecting homes for over 57 years. He manages and trains a team of service pros while also leading internal research efforts—recently spearheading a deep-dive review of thousands of documents on pest control materials to hand-pick the most kid and pet friendly, most effective solutions tailored specifically for homes in the DC metro area.