Tree mites are tiny arachnids, related to spiders and ticks, that feed on the sap of plants, trees, and shrubs. The term “tree mite” covers a variety of species responsible for damaging foliage. Identifying them requires recognizing their physical form and the specific signs they leave behind.
Shared Physical Traits of Tree Mites
Tree mites are challenging to see with the naked eye, as adults typically measure less than a millimeter. Under magnification, their body shape is generally oval or pear-shaped, distinguishing them from the elongated forms of many insects.
As arachnids, adult mites possess eight legs, while newly hatched larvae initially have only six. They lack antennae or wings, which differentiates them from small flying insects.
Their color is highly variable, often determined by the species and the type of plant they are feeding on. Colors range from red and reddish-brown to pale green, yellow, or black, making color alone insufficient for identification.
Distinctive Features of Common Species
Spruce Spider Mites
Spruce spider mites are active during the cooler temperatures of spring and fall. Visually, these mites are dark green to almost black, sometimes appearing reddish-green, and measure about 0.5 millimeters in length. They are often found on conifers, such as spruce, pine, and fir, where their feeding causes stippling or mottling on the needles.
Clover Mites
Clover mites are reddish-brown or bright red, often leading them to be mistaken for small spiders. A distinguishing feature is their front pair of legs, which are significantly longer than the other six and project forward. These mites rarely exceed 0.75 millimeters and often invade structures in large numbers during the spring and fall.
Oak Mites (Itch Mites)
Oak mites are nearly invisible to the unaided eye, measuring only about 0.2 millimeters long. Visual identification of the mite itself is impractical due to its microscopic size. An infestation is usually first indicated by a rash or bites on humans rather than by seeing the pest. These reddish-tan mites are associated with pin oak trees, where they feed on larvae within leaf galls.
Observable Habits and Habitat Clues
Observing the location and behavior of mites provides important clues. Many plant-feeding mites prefer to congregate on the undersides of leaves, especially in the lower canopy, where they are protected from direct sunlight.
A simple method to check for their presence is the “white paper test.” A branch is shaken over a white surface to see if tiny specks—the mites—fall off and begin to move. The speed of movement can also offer a clue, as some species move quickly while others are more sluggish.
Evidence of their feeding includes fine, pale speckling or stippling on the leaves, caused by the mites sucking out plant fluids. Furthermore, some species, particularly spider mites, produce fine, silky strands of webbing that become noticeable in severe infestations, often covering needles and twigs.