Spider Mites Identification Guide

Spider Mites Identification Guide

Physical Characteristics

Spider mites are very small arachnids. They measure between 0.2 and 0.5 millimeters long. You can barely see them without a magnifying glass. They often look like tiny moving specks on plant leaves. Adult spider mites have eight legs, which sets them apart from insects that have six.

Their color varies by species. They can be red, reddish-brown, yellow, green, or orange. The twospotted spider mite is the most common type. It has a yellowish or greenish body with two dark spots on its back. Color can change based on diet and time of year. Some species turn reddish-orange before winter.

Spider mites have oval bodies and spin fine silk webbing. This webbing is often the first sign of an infestation. It helps protect the mites from threats and harsh weather.

Common Species in North America

Twospotted Spider Mite (Tetranychus urticae): This is the most common species. It feeds on over 180 plant types including vegetables, fruits, and flowers. Adults are pale yellow to greenish with two dark spots on their backs.

Spruce Spider Mite (Oligonychus ununguis): This mite attacks evergreens like spruce, juniper, and arborvitae. It is most active in spring and fall, not summer.

European Red Mite (Panonychus ulmi): This mite mainly attacks fruit trees like apples and pears. Adult females are dark red with white spots.

Pacific Spider Mite (Tetranychus pacificus): Found in western North America. It affects grapes, almonds, and many ornamental plants.

Spider Mites Behavior and Biology

Habitat and Host Plants

Spider mites live mostly on the undersides of plant leaves. They feed by piercing plant cells and sucking out the contents. They attack many plants including vegetables like beans, tomatoes, and peppers. They also feed on fruits like strawberries and melons, plus houseplants and trees.

These mites prefer hot, dry conditions. They cause the most problems during summer droughts. Plants that lack water are more likely to suffer damage. Stressed plants cannot replace lost fluids fast enough.

Feeding and Damage

Spider mites use tiny mouthparts to puncture plant cells and suck out the contents. This includes chlorophyll, which gives leaves their green color. Feeding creates tiny white or yellow dots on the upper leaf surface. This damage pattern is called stippling. As damage adds up, leaves may turn bronze, yellow, or brown. They may drop from the plant.

Bad infestations can strip leaves from entire plants. This reduces crop yields and can kill ornamental plants. The silk webbing they make can cover leaves and stems. This gives plants a dusty or dirty look.

Reproduction and Life Cycle

Spider mites multiply fast in good conditions. A female can lay 100 to 200 eggs in her 2-4 week life. She deposits up to 20 eggs per day on the undersides of leaves. Eggs are round and start out clear. They turn whitish as they get ready to hatch.

The life cycle has four stages: egg, larva (with six legs), nymph (with eight legs), and adult. In warm weather around 80-90 degrees, the cycle can finish in just 5-7 days. This fast breeding means populations can grow quickly. Multiple generations overlap during the growing season.

Spider mites have a unique breeding system. Unfertilized eggs produce males. Fertilized eggs produce females. This means even one female can start a new colony.

Treatment Methods for Spider Mites

Spider mites mainly affect gardens, landscapes, and crops rather than structures. Control efforts focus on protecting plants through several methods.

Cultural Controls

• Keeping Plants Healthy: Water plants well and avoid drought stress. This makes plants stronger against spider mite damage. Healthy plants recover faster from feeding.

• Humidity Control: Spider mites love dry conditions. Misting houseplants or using drip irrigation can slow mite growth.

• Removing Infested Material: Take off heavily infested leaves or plants. Throw them away from other plants to stop the spread.

• Balanced Fertilizing: Too much nitrogen creates soft growth that spider mites prefer. Use balanced fertilizer to reduce risk.

Physical Controls

• Water Sprays: Strong water sprays aimed at the undersides of leaves knock mites off and break up their webbing. This works best for light infestations. You need to repeat it often.

• Pruning: Cut off heavily infested plant parts. This reduces mite numbers before they spread to the rest of the plant.

Biological Controls

• Predatory Mites: Some mites eat spider mites. Species like Phytoseiulus persimilis can be bought and released onto infested plants.

• Other Predators: Lady beetles, lacewing larvae, and minute pirate bugs feed on spider mites and can help reduce populations.

Chemical Controls

• Insecticidal Soaps: These products break down mite cell walls. They work when applied directly to mites.

• Horticultural Oils: Petroleum or plant-based oils coat and suffocate mites and eggs. Apply them well to leaf undersides where mites live.

• Miticides: These are pesticides made for mite control. They work for severe infestations. Spider mites can develop resistance quickly, so rotate between different products.

Preventing Spider Mite Infestations

• Inspect new plants before bringing them home or into the garden
• Quarantine new houseplants for 2-3 weeks before placing them near other plants
• Maintain adequate soil moisture and avoid drought-stressing plants
• Avoid placing plants near heat sources or in hot, dry locations
• Remove weeds around gardens, as they can harbor mite populations
• Space plants properly to improve air circulation

References

• Spider Mites - UC Statewide Program
• Spider Mites and Their Control - Ohio State University Extension
• Spider Mite Control - Clemson Cooperative Extension
• Twospotted Spider Mite - University of Minnesota Extension
• Spider Mites - Colorado State University Extension