Spider Mites (Family Tetranychidae): Identification, Risks & Control

The Spider Mites (Family Tetranychidae) are among the most destructive plant pests across the globe. Despite their tiny size, these arachnids (not insects) feed by piercing plant cells and sucking out sap, leaving behind weakened plants, reduced yields, and in severe cases, complete crop failure.

The most notorious species is the Two-Spotted Spider Mite (Tetranychus urticae), a highly polyphagous pest found on more than 200 plant species. But other damaging species include the Carmine Spider Mite (Tetranychus cinnabarinus) and the Southern Red Mite (Oligonychus ilicis).

Unlike storage pests such as the Cigarette Beetle (Lasioderma serricorne) or the Drugstore Beetle (Stegobium paniceum), spider mites attack living plants. They are especially problematic in hot, dry environments where their populations can skyrocket, making them one of the top greenhouse and field pests worldwide.

Identification

Adults

• Size: less than 0.5 mm.

• Body: oval, with eight legs (a key distinction from six-legged insects).

• Colors: green, yellow, orange, or red depending on species and season.

• Distinctive sign: fine silk webbing across leaves and stems.

Eggs

• Round, translucent to whitish.

• Deposited on the undersides of leaves.

Nymphs

• Smaller versions of adults, also with eight legs.

• Pass through larval and nymphal stages before becoming reproductive adults.

Field signs

• Fine webbing across plants.

• Tiny moving dots (mites) visible with a hand lens.

• Stippled, pale leaves that lose vigor.

Biology and Lifecycle

Spider mites thrive under conditions that stress plants: high temperatures and low humidity.

• Egg stage: Hatch in 3–5 days in warm weather.

• Larval/nymphal stages: Last 5–10 days, feeding actively on plant tissue.

• Adult stage: Females live 2–4 weeks, producing 50–100 eggs.

Favorable conditions

• Temperatures above 27 °C (80 °F) accelerate reproduction.

• Dry environments reduce natural fungal enemies, boosting outbreaks.

• Under greenhouse conditions, populations can multiply year-round.

Because each generation can mature in under 2 weeks, infestations often explode before growers notice the early signs.

Ecology and Distribution

• Found worldwide, from tropical to temperate climates.

• Thrive in greenhouses, open fields, orchards, and ornamental gardens.

• Attack a wide range of hosts including beans, cucumbers, peppers, tomatoes, strawberries, roses, cotton, and fruit trees.

• Frequently coexist with Thrips, Aphids, and Whiteflies, causing complex mixed infestations.

Risks and Damage

Spider mites weaken plants both directly and indirectly.

• Stippling: Tiny white or yellow dots on leaves from sap removal.

• Webbing: Dense silk that reduces light interception.

• Photosynthesis loss: Leaves yellow and drop prematurely.

• Crop yield reduction: Lower fruit and vegetable production.

• Plant death: Severe infestations can kill seedlings and annuals.

• Disease vector: Feeding wounds may allow fungal and bacterial pathogens to enter.

In greenhouses and high-value crops, economic losses can be enormous.

Signs of Infestation

• Pale, speckled leaves.

• Fine webbing on foliage.

• Visible mites moving on undersides of leaves.

• Plants showing stunted growth and reduced vigor.

• Entire sections of crops turning yellow or brown.

Household and Garden Control

For houseplants and small gardens, management usually combines cultural, biological, and natural treatments.

• Water management: Increase humidity around plants; spider mites dislike moist air.

• Pruning: Remove heavily infested leaves.

• Showering: Wash plants with water to dislodge mites.

• Oils and soaps: Neem oil, horticultural oils, and insecticidal soaps suppress populations.

• Biological control: Predatory mites (Phytoseiulus persimilis) are highly effective.

Spider mites often appear alongside Fungus Gnats in overwatered houseplants, making dual management necessary.

Industrial and Professional Control

In agriculture and greenhouse production, spider mites are one of the toughest pests to manage.

Monitoring

• Regular scouting with hand lenses.

• Yellow sticky traps for related pests (Whiteflies, Thrips) to anticipate outbreaks.

Biological control

• Predatory mites (Neoseiulus californicus, Phytoseiulus persimilis).

• Lady beetles and lacewings may help suppress populations.

Cultural practices

• Maintain proper irrigation to avoid drought stress.

• Rotate crops and remove infested residues.

• Maintain greenhouse humidity above 60%.

Chemical control

• Miticides are available but must be rotated to prevent resistance.

• Overuse leads to resistant strains of Tetranychus urticae.

• Selective chemicals preferred to preserve beneficial insects.

Integrated Pest Management (IPM)

• Combining monitoring, sanitation, biological enemies, and selective miticides provides long-term stability.

Case Study: Greenhouse Tomato Infestation

A Mediterranean tomato greenhouse experienced massive losses due to Two-Spotted Spider Mite (Tetranychus urticae).
Leaves yellowed, webbing spread across plants, and fruit production dropped by 40%.

The management strategy included:

• Introducing predatory mites early in the season.

• Increasing humidity levels.

• Rotating selective miticides to avoid resistance.

• Removing crop residues after harvest to eliminate overwintering sites.

Within one growing cycle, infestations were suppressed, and yields returned to profitable levels.

FAQ

Q: Are spider mites insects?
A: No, they are arachnids, related to spiders and ticks.

Q: Do spider mites bite humans?
A: No, they do not feed on humans, though heavy infestations may cause skin irritation when handling plants.

Q: What crops are most affected?
A: Vegetables (tomatoes, cucumbers, beans), fruits (strawberries, melons), and ornamentals (roses, houseplants).

Q: Can spider mites kill plants?
A: Yes, severe infestations can kill seedlings and cause crop losses.

Q: What are natural predators of spider mites?
A: Predatory mites such as Phytoseiulus persimilis are the most effective.

Final Thoughts

The Spider Mites (Family Tetranychidae), especially the notorious Two-Spotted Spider Mite (Tetranychus urticae), prove that some of the most devastating plant pests are also the smallest. Unlike storage pests such as the Flour Beetles or Rice Weevil, these mites feed directly on living plant tissues, weakening crops from within.

For home gardeners, spider mites are usually more of a frustration than a disaster—yet if left unchecked, they can destroy entire collections of houseplants. For greenhouse growers and large-scale farms, however, the risks are massive: crop losses, chemical resistance, and the need for expensive biological or chemical controls.

The lesson is clear: early detection and Integrated Pest Management (IPM) are essential. Monitoring plants regularly, applying cultural practices like humidity management, introducing natural predators, and using miticides only when necessary can keep populations under control.

In agriculture, spider mites will likely remain a challenge due to climate change, which favors the hot, dry conditions they love. Still, with science-backed strategies and vigilance, growers can minimize their impact and protect plant health.

Read more in our blog and explore guides on many other enemies. Stay informed.

Disclaimer

This article is for informational purposes only. Pest control laws and approved chemicals vary by country. For best results and legal safety, we strongly recommend contacting a licensed pest control professional in your local area. Always make sure that the pest control technician is properly certified or licensed, depending on your country’s regulations. It’s important to confirm that they only use approved products and apply them exactly as instructed on the product label. In most places in Europe, UK, or USA, following label directions is not just best practice—it’s the law.

Author

Nasos Iliopoulos
MSc Agronomist & Certified Pest Control Expert
Scientific Director, Advance Services (Athens, Greece)
Licensed Pest Control Business – Ministry of Rural Development & Food (GR)

References

• Wikipedia – Spider Mites

• University of Minessota – Twospotted spider mites in home gardens

• Penn State Extension – Two-Spotted Spider Mite Fact Sheet

• Royal Horticultural Society – Spider Mites on Ornamentals

• North Carolina State University Extension – Greenhouse Pest Management