Spruce Spider Mite
Oligonychus ununguis

Mites are not insects. Adults have eight legs and are extremely small (0.58 mm long). Their bodies are dark green to almost black with a pale streak on the middle of the back. Females have a more oval abdomen than males. Eggs, yellow to reddish-brown in color, are spherical (0.2 mm in diameter) with a spike that anchors them to the webbing. Eggs hatch into six-legged larvae that turn from pink to green after feeding. Larvae grow into eight-legged nymphs (0.3 to 0.4 mm long) that resemble the adults.

Identification:

This oval-shaped mite is small (about 1/50”), and with all eight legs stretched out would just cover the period at the end of this sentence. Considerable color variation exists depending upon its age, time of the year and host plant. Newly hatched larvae are pinkish in color, but turn dark green or dark red after initial feeding. The overwintering red eggs are found on the bark of small branches on the host plant. Many spider mites produce webbing, particularly when they occur in high populations, providing protection from natural enemies and heavy rainfalls.

Injury:

Mites suck on the older needles of trees, causing fine stippling that increases in intensity until the foliage lacks chlorophyll and has a bleached appearance. Severely infested foliage becomes yellowish or brownish and many needles drop. Damage is most severe in lower crowns of large trees. Seedlings and small trees often are killed, and in some cases, large trees are killed. The mites spin a webbing of fine silk around twigs and needles that becomes more abundant as the season progresses. Damage is most severe during the spring and fall. Although mite populations build up most in cool weather, hot, dry weather predisposes trees to attack.

Biology and History:

Five to eight generations occur annually. Overwintering eggs are placed on the undersides of twigs and needles. Egg hatch occurs in mid-April and several generations of mites may occur before hot summer weather begins in late June. Mite activity begins again in late September and continues until winter weather starts in November. One generation may take as few as ten to 14 days. Mites can disperse on wind currents, by adults crawling from tree to tree, and on nursery stock.