The red spider mite, more accurately known in the United States as the two-spotted spider mite (Tetranychus urticae), is one of the most common and destructive mite pests of plants. It is widespread in greenhouses, gardens, landscapes, agricultural crops, and houseplants. Because of its extremely broad host range and rapid reproduction, it is a major concern for both home gardeners and commercial growers.
This article explains where spider mites occur, what they feed on, how to identify infestations, and how they are most effectively controlled under U.S. conditions.
Occurrence and Host Plants
Two-spotted spider mites attack more than 200 plant species, making them one of the most versatile plant pests.
They commonly infest:
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Greenhouse crops
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Houseplants
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Garden plants and ornamentals
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Trees and shrubs
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Fruit trees and berry bushes
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Vegetable crops
In greenhouses, they are especially problematic on cucumbers, tomatoes, beans, peas, and lettuce. Outdoors, they are frequently found on strawberries, blueberries, currants, roses, and many ornamental plants.
Spider mites thrive in warm, dry environments, which is why infestations often explode during hot summers or in heated greenhouses.
Feeding Behavior and Plant Damage
Spider mites feed by piercing plant cells with needle-like mouthparts and sucking out the contents.
Typical damage includes:
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Fine, pale stippling on leaves
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Leaves turning grayish, yellow, or bronze
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Dead patches where plant tissue has collapsed
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Leaf drop in severe infestations
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Browning and wilting of flower petals
All life stages produce fine webbing on infested plants. The webbing protects eggs and helps mites move between leaves and neighboring plants.
Without control, heavily infested plants may lose most or all foliage.
How to Identify Spider Mites
Spider mites are extremely small and difficult to see with the naked eye.
Identification methods include:
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Using a hand lens or magnifying glass to inspect the underside of leaves
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Looking for mites, webbing, shed skins, and eggs on leaf undersides
A very effective test:
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Hold a white sheet of paper under a leaf
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Tap or scrape the underside of the leaf
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Mites fall onto the paper and appear as tiny moving dots
Spider mites may be greenish, yellow, orange, red, or brown. On plants, they are usually almost invisible without magnification.
Reducing Spider Mite Populations Quickly
Remove Heavily Infested Leaves
Pruning and destroying the most heavily infested leaves can quickly reduce population pressure. Removed plant material should be sealed and discarded immediately to prevent spread.
Biological Control – The Most Effective Method
Biological control is the cornerstone of spider mite management, especially in greenhouses.
The most effective natural enemies are predatory mites, particularly:
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Phytoseiulus persimilis (specialist spider mite predator)
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Amblyseius cucumeris
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Orius species (minute pirate bugs)
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Green lacewing larvae (Chrysoperla species)
Phytoseiulus persimilis is the most widely used predator and can consume up to 20 spider mite eggs or 5 adult mites per day. It is highly effective when introduced early and under favorable conditions.
Predatory mites can be distinguished from spider mites by:
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Longer legs
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Faster movement
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Greater overall activity
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Often red or orange coloration
Temperature and Humidity Management
Environmental conditions strongly influence spider mite populations.
To slow reproduction:
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Lower temperatures where possible
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Increase relative humidity around plants
High humidity suppresses spider mite development and favors natural enemies. Unfortunately, complete prevention is not possible, but environmental management greatly reduces pressure.
Spider Mites in Greenhouses
In greenhouses, spider mites are often referred to as greenhouse spider mites, but they are the same species found on houseplants and outdoor crops.
Management in greenhouses typically relies on:
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Early detection
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Repeated release of predatory mites
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Environmental control
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In severe cases, spot treatment with insecticidal soap
Spider Mites on Houseplants
On houseplants, infestations can often be managed with less aggressive measures.
Effective steps include:
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Regularly spraying plants with water to physically knock mites off
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Paying special attention to leaf undersides
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Increasing humidity around plants
If water alone is insufficient, insecticidal soap can be used carefully on affected plants.
Control Products for Spider Mites
In practice, insecticidal soap is the only widely recommended direct-control product for spider mites.
Important considerations:
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It kills mites on contact, including beneficial predators
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It should be used only on infested plants
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Overuse can disrupt biological control
For this reason, biological control with predators is usually the preferred long-term solution.
Life Cycle of the Two-Spotted Spider Mite
Spider mites pass through four life stages:
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Egg
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Larva
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Nymph
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Adult
Under hot, dry conditions, development from egg to adult can occur in 5–7 days. At moderate temperatures (around 78°F / 26°C), development takes about 10 days. In cooler outdoor conditions, development may take 15–20 days.
Egg Stage
Females lay 50–200 eggs during their lifetime. Unfertilized eggs develop into males, while fertilized eggs become females. Eggs are round, translucent, yellowish, and extremely small (about 0.13 mm). They are held in place by webbing.
Larval Stage
Larvae have six legs and are nearly colorless. They feed only lightly during this stage.
Nymph Stage
Nymphs have eight legs and resemble small adults. They pass through two stages (protonymph and deutonymph) before reaching maturity.
Adult Stage
Adults have eight legs and vary in color from greenish-yellow to orange, red, or brown. Overwintering females are typically orange to red. Females are larger than males. Two dark spots are often visible through the body, representing internal waste material.
Overwintering and Seasonal Development
Adult females overwinter in:
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Grass lawns and fields
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Roadside vegetation
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Weedy areas
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Leaf litter
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Tree bark crevices
In spring, they begin feeding on grasses and weeds before moving onto cultivated plants. Reproduction continues throughout the growing season.
Effect of Weather on Spider Mites
Weather strongly influences spider mite outbreaks.
Hot, dry conditions favor spider mites because:
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Development time is shortened, producing more generations
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Natural fungal pathogens are reduced
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Predator populations decline
Spider mite populations are therefore closely linked to temperature and humidity, with drought conditions posing the greatest risk for severe infestations.
Consistent monitoring, early intervention, and biological balance are the most effective strategies for managing spider mites over the long term.