Plant mites are minute creatures that can cause significant damage to houseplants, garden vegetables, and ornamental shrubs. These pests are classified as arachnids, meaning they are structurally related to spiders and ticks, not insects. They use specialized piercing-sucking mouthparts to penetrate plant cells, particularly on the undersides of leaves, and then consume the internal cellular contents. This feeding action disrupts the plant’s ability to photosynthesize, leading to visible damage that often alerts a plant owner to their presence.
The Visual Basics of Plant Mites
Most plant mites are incredibly small, measuring less than half a millimeter, making them difficult to detect without magnification. When viewed closely, the body is typically oval or pear-shaped. Mites lack the distinct three-part division (head, thorax, and abdomen) found in insects.
Adult mites possess eight legs, a definitive characteristic of the arachnid class. This sets them apart from true insects, which have only six legs in their adult stage. While mite larvae start with six legs, they molt into nymphs and adults that feature four pairs of walking legs.
Key Identification Features of Common Mite Species
The appearance of phytophagous (plant-feeding) mites varies considerably by species, with some being visible and others requiring a microscope. The most frequently encountered are spider mites, which can range in color from pale green or yellow to red, depending on their food source and the time of year. The two-spotted spider mite, a common pest, is identifiable by the two dark spots visible on its back, one on each side of the body.
Other common species are the broad mite and the cyclamen mite, which are nearly impossible to see with the naked eye. They are generally less than 0.3 millimeters long and have a translucent or glassy appearance. Their presence is usually confirmed by the unique damage they inflict rather than by spotting the pest itself.
Eriophyid mites, including rust mites and gall mites, have a distinct form. These are the smallest of the group, with an elongated, worm-like, or cigar-shaped body that is less than 0.25 millimeters long. Uniquely, eriophyid mites only possess four legs, which are clustered near the head end of their body.
Evidence of Their Presence on Plants
Since mites are too small to see clearly, the first sign of an infestation is typically the damage they leave behind on the plant tissue. The most common symptom is stippling, which appears as fine, pale, or yellowish pinprick dots on the leaf surface. This discoloration occurs where the mites have pierced individual plant cells and removed the chlorophyll-containing contents.
In severe infestations, the stippling can merge together, causing the entire leaf to take on a bronzed, silvery, or bleached appearance. Spider mites produce fine, silky strands of webbing, which they use for shelter. This webbing is often most visible between leaf petioles and the stem or on the undersides of leaves.
Certain microscopic mites, such as broad mites and cyclamen mites, inject toxic saliva while feeding, which causes new growth to become deformed. This damage manifests as stunted, thickened, or twisted leaves, often with a brittle texture and a bronzed appearance. Another sign is the presence of tiny, whitish specks, which are the shed exoskeletons or cast skins.
Distinguishing Mites from Other Pests
When small pests are found on a plant, it is important to confirm that they are mites and not another type of pest, which may require a different treatment approach. The most reliable way to differentiate adult mites from insects like aphids, thrips, or fungus gnats is by observing the number of legs. Mites have eight legs, while adult insects have six legs and often possess wings, which mites never do.
Aphids, for instance, are generally larger than most mites and have visible antennae and two small, tube-like structures called cornicles projecting from their abdomen. Thrips are slender, often dark-colored insects that have fringed wings in the adult stage. The easiest way to check if tiny specks are living mites is to tap an affected leaf over a clean white sheet of paper.
Living mites dislodged from the plant will appear as small, dark specks against the white background and will begin to slowly crawl away. If the specks do not move, they are likely debris, dirt, or shed cast skins. This simple method helps confirm the presence of a mobile pest population.