Spider mites are tiny arachnids, closely related to ticks and spiders. These common garden and houseplant pests are often described as microscopic, but adult spider mites can be seen with the unaided eye, appearing as little more than moving specks. Because they are difficult to see, an infestation often goes unnoticed until the damage to the plant becomes severe.
Physical Appearance and Direct Visibility
Adult spider mites are minute, typically measuring less than 1 millimeter in length, making them about the size of a period or a grain of pepper. Their bodies are oval-shaped with eight legs, classifying them as arachnids. Their small stature and tendency to congregate on the undersides of leaves make direct observation difficult. The color of a spider mite can vary significantly depending on the species and what they have been feeding on. The common two-spotted spider mite is often pale green or yellow with two dark spots, though other species can be red, orange, or nearly transparent.
Recognizing the Indirect Signs of Damage
Since the mites themselves are so small, the damage they cause is often the first recognizable sign of their presence. Spider mites feed by piercing plant cells and sucking out the chlorophyll and cell contents. This feeding action leaves behind a distinctive pattern of tiny, pale spots on the leaves, a symptom known as stippling. Stippling appears as small yellow or white dots on the upper surfaces of the leaves. Severe infestations cause the entire leaf to take on a dull, yellow, or bronze cast, often leading to premature leaf drop.
A primary indicator of spider mites is the fine, silky webbing they produce, which gives them their common name. This webbing is much finer than a spider’s web and is typically found along the veins of leaves, on the undersides, or strung between leaves and stems. Other indirect evidence includes tiny, clear eggs and whitish, translucent shed exoskeletons (cast skins) left behind after molting.
Simple Techniques for Confirmation
If you suspect an infestation based on stippling or webbing, a simple method called the “White Paper Test” can confirm their presence. Place a clean sheet of white paper underneath the affected leaf or stem cluster and gently tap the plant to dislodge any pests. Specks that fall onto the white surface should be observed closely; if they are spider mites, they will begin to crawl around. Rubbing the specks to see if they leave a reddish or greenish streak is a strong indication of crushed mites.
Using Magnification
To get a clearer view of the mites or their eggs, a simple hand lens or jeweler’s loupe is an effective tool. A magnification of 10x to 20x is usually sufficient to see the mites’ oval bodies and eight legs, confirming their identity. Checking the undersides of leaves with this magnification will reveal the pests, their eggs, and the fine webbing.