Scale are small soft-bodied insects that cover themselves with layers of either flexible or stiff wax. These covers help them blend into their environment, prevent them from drying out, and hide them from predators. For gardeners, this shield also blocks most contact insecticides from touching the insect itself.
Typical wax colors are brown, gray, or white, though the insect underneath can be more colorful – rosy-red or purplish. Cover shapes are usually round, rice-shaped, or oystershell-shaped, and are often smaller than a third of an inch (8-9 millimeters). Scale enlarge their covers as they grow, though, in some species, male and female covers can be different sizes, shapes, and colors.
As a gardener and plant enthusiast, I’ve dealt with my fair share of plant pests. One of the most annoying to identify and control is scale insects. These tiny sap-sucking bugs can quickly get out of control, damaging ornamental plants and crops.
In this article, we’ll take a deep dive into the different types of scale insects, how to identify them, their appearance, and most importantly – how to control these tricky pests.
What Are Scale Insects?
Scale insects are very small bugs, from 1/16 to 1/4 inch long when mature, that feed on plant sap. They are closely related to aphids and whiteflies. There are around 8,000 known species.
These insects get their name from the protective waxy or cottony covering they produce, which resembles fish scales or reptile skin. This covering shields the insect underneath.
Female scales are usually immobile and wingless, with reduced or no legs and antennae. They look nothing like a normal insect! Males are more gnat-like but cannot feed.
Scale insects pierce the plant tissue and suck out sap. This can stunt growth, cause leaf yellowing, and even kill branches. Their sweet honeydew secretions also promote sooty mold growth.
However, a few scales like cochineal are farmed for natural dyes and shellac. Some species are used as biocontrols for invasive cacti
Scale Insect Identification
Identifying scale insects can be tricky given their tiny size and protective covers, Look for
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Small bumps or lumps on stems and leaves. Common on undersides.
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Discolored/yellowing foliage or premature leaf drop.
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Sticky honeydew and sooty mold on leaves.
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Cottony tufts or waxy shells on stems.
Use a magnifier to inspect bumps and remove covers. Look for the scale insect body underneath.
There are two main scale insect groups – armored (hard cover) and soft (waxy cover). Species vary widely in shape, size and color.
Types of Scale Insects
There are hundreds of scale insect species. Here are some of the most common types you may encounter:
1. Cottony Cushion Scale
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Flattened, red-brown scales in white fluffy egg sacs.
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Feed on citrus, woody plants.
2. Cochineal
- Red/purple scales on cacti. Farmed for natural dyes.
3. Beech Scale
- Tiny white scales on beech trees.
4. Euonymus Scale
- Gray-brown scales on euonymus shrubs.
5. Brown Soft Scale
- Small brown bumps on houseplant leaves.
6. Cottony Maple Scale
- Large white egg masses on soft maple branches.
7. Hemispherical Scale
- Brown domed bumps on houseplant leaves.
8. San Jose Scale
- Circular gray scales with central dot on fruit trees.
9. Oystershell Scale
- Elongated brown scales on ash, lilac.
10. Pine Needle Scale
- White scales that encrust pine needles.
As you can see, scale insects come in many shapes, sizes and colors. Proper identification is key to control. A hand lens helps inspect them closely.
Controlling Scale Insects
Getting rid of scale insects requires persistence. Their waxy covers protect them from sprays. Key control methods include:
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Monitoring plants regularly and quickly treating new infestations before they spread.
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Pruning out heavily infested stems and leaves.
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Using a soft brush or cotton swab dipped in alcohol to rub them off. Avoid wetting soil.
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Applying horticultural oils and insecticidal soaps to suffocate scales. Target crawlers for best results.
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Using systemic insecticides for heavy infestations. Take care as some can damage plants.
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Releasing natural predators like ladybugs and parasitic wasps which feed on scales.
With diligent monitoring and multiple applications of insecticides, oils, or soapy water, scale infestations can usually be controlled. Discard badly infested plants.
Prevention is best – inspect new plants thoroughly before buying and quarantine if needed. Stop scales before they spread! With appropriate identification and control measures, you can keep these sneaky sap-suckers from damaging your precious plants.
Features of scale life cycles
- Mature female scale do not have wings. Mature males are winged in order to find mates, but they are so tiny that they are rarely seen.
- Females lay eggs either entirely under their protective covers or under an additional secretion of fluffy, cottony wax.
- Mature females die after laying eggs. Generally, soft scale have one generation per year, while armored scale have several, though there are exceptions.
- When eggs hatch, the newborns are called crawlers because they actively wander around to find a place to feed. They do not have covers for protection. Once they choose a spot, they either rarely move or stay put for the rest of their lives; at this point, they are referred to as “settled.”
- As they grow, these settled crawlers quickly develop their waxy shell and, for some species, lose their legs.
Cottony Maple Scale laying eggs in a fluffy, waxy ovisac next to her body Photo: D.K.B Cheung
Fletcher Scale female lifted to show eggs underneath her cover. Photo: Brian Kunkel, University of Delaware, Bugwood.org
Examples of armored scale
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Euonymus scale
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White prunicola scale
The COMPLETE Guide to Getting Rid of Scale Insects
FAQ
What kills scale insects?
A well-timed and thorough spray of horticultural (narrow-range) oil during the dormant season, or soon after scale crawlers are active in late winter to early …
How do you identify a scale bug?
Scale Identification
At first glance, many scale insects look like a small, circular bump that’s part of the plant. Depending on the species, they vary in color from brown to cottony white and measure up to 1/4 inch long. Scale nymphs are known as crawlers and are similar in appearance.
How many species of scales are there?
Scale insects are a diverse group of insects in the order Hemiptera. There are about 6,000 species of scale insects in 21 families worldwide.
What is the difference between hard scale and soft scale?
Hard scales tend to be flatter, don’t move once mature, and don’t excrete much honeydew. Soft scales are generally more hump-shaped, slowly move while feeding (slow being the key word), and excrete large amounts of honeydew.
What is a scale insect?
Scale insects are a large and diverse group (about 8,000 described species) in the superfamily Coccoidea of the order Hemiptera, closely related to aphids and whiteflies, but they look quite different from your typical insect (the mealybugs are part of this superfamily, too, but are not included in this article).
How do scale insects feed?
Scale insects feed by inserting small, straw-like mouthparts into plants to suck out nutrients. Because scales feed on dark parts of the plant like the bark, it’s easy for certain species and types of scale insects to blend in. There are two main types of scale insects, armored scales and soft scales.
How many types of scale insects are there?
There are hundreds of types of scale insects you can encounter. Most of them have a drastically different appearance. Feeding on plants, scale insects can even be found indoors. Part of the Homoptera order, scale insects can be found all around the world, especially on crops or in areas of thick vegetation with plenty of plants.
How big do scale insects grow?
They grow from 2.5mm to 3.5mm but they can reach a size of up to 6mm when they start to cover their bodies in soft wax. There are hundreds of types of scale insects you can encounter. Here are 37 types of scale insects that can damage your plants.
What colors do scale insects come in?
Scale insects come in all colors such as white, gray, green, and brown. 1. Cottony Cushion Scale This small-scale insect (Icerya purchasi) measures up to 5mm.
Where can scale insects be found?
Feeding on plants, scale insects can even be found indoors. Part of the Homoptera order, scale insects can be found all around the world, especially on crops or in areas of thick vegetation with plenty of plants. What Are Scale Insects?