Pest profile

Spruce Spider Mite

Oligonychus ununguis · Trombidiformes: Tetranychidae[3]

The spruce spider mite is one of the most destructive spider mites in the US, speckling and browning the needles of spruce, arborvitae, juniper, hemlock and other conifers.[1]

No licensed photo of this species is available yet; the identification notes below describe what to look for.

How to identify it

  • Adults and nymphs are dark green to nearly black with salmon-pink spines and salmon-pink legs, about 0.5 mm long.[1]
  • Infested trees look speckled and yellowish at first, and the mites spin silk webs on the needles.[1]

Where it lives

Penn State Extension covers it on landscape conifers in Pennsylvania; dwarf Alberta spruce is a preferred host.[1]

US map: public records from 3 states since 1990 (GBIF).

Biology and life cycle

It overwinters as brown eggs around bud scales and needle bases, which hatch in spring before new growth starts.[1]

A generation takes 15 to 20 days, with 7 to 10 a year; it's considered a cool-season pest.[1]

Damage and signs

  • Feeding on older, inner and lower needles turns them rusty, and they may drop early.[1]

Health risk

It feeds on plants; Penn State Extension mentions no risk to people.[1]

Control

Prevention

Hold white paper under a branch and strike it; ten or more dark mites at each of three or four spots means treatment is warranted.[1]

Pesticides

Treat in early to mid-May and again in early September if needed, and rotate miticide classes after every third application to slow resistance.[1]

More from NC State Extension

Each egg has a thin thread sticking up from its center, which identifies the species; only the eggs survive hot summers and very cold winters, so most reproduction happens in spring and fall.[2]

Common questions

Why is my dwarf Alberta spruce turning rusty brown inside?
Spruce spider mites often attack its older, inner needles, which turn rusty and drop.[1]
How do I check a conifer for spider mites?
Tap a branch over white paper and look for tiny dark mites moving on it.[1]

Sources

  1. Penn State Extension, “Spruce Spider Mite.” extension.psu.edu/spruce-spider-mite (accessed 2026-10-06)
  2. NC State Extension, “Spruce Spider Mite.” content.ces.ncsu.edu/spruce-spider-mite (accessed 2026-10-15)
  3. iNaturalist, “Oligonychus ununguis taxon page (order and family).” www.inaturalist.org/taxa/263173 (accessed 2026-10-06)

Updated 2026-10-15. Built from sourced records. Spot an error? Tell us.