Adelgids are related to aphids, but are in their own family, as Adelgids are only attracted to conifers.

What are Spruce Galls?

With their sucking mouth-parts, these adelgids feed on plant juices, causing an irritation that results in plant tissue developing into cone-like galls characteristic in form and shape. Continued infestations disfigure both ornamental and Christmas trees, weakening them, and making them subject to attack by other pest organisms.

What Adelgids make galls?

There are three Adelgids that cause galls on spruce trees, one however does not have the spruce tree it would infest in this country. That one the Wooly Hemlock, which does negatively affect with galls, the Hemlock tree.

Eastern Spruce Gall Adelgid: Galls caused by this insect occur mostly on Norway, white, black, and red spruce trees as well as other spruce. An infestation does not spread rapidly from one tree to another. It is not unusual to find specific trees in a planting rather heavily infested year after year while others of the same species may escape injury. There is also a wide range of resistance to this insect within the same tree species.

The eastern spruce gall adelgid spends winter as an immature female, usually located in a crevice at the base of a spruce bud. The adult female is a small, bluish-green, sucking insect covered by cottony, waxy strands. The eggs are dark olive-green to black and oval shaped. Nymphs range in color from yellow to blue green and can grow to about 1/8 inch long.

  • It begins feeding in early spring and in May it deposits a mass of eggs covered with waxy threads.
  • The eggs hatch when the shucks break away from the bud and expose the new needles.
  • The newly hatched adelgids crawl into the mass of new needles to feed.
  • The swelling needle bases develop into a compact mass and form a pineapple-shaped gall. Each gall has many individual cells, inhabited by many adelgids.
  • In late September, the cells open and the adelgids escape. These escapees produce the individuals which live through winter.

Since its introduction from Europe before 1900, it has spread throughout the northeastern US and southern Canada. The adelgid, which is closely related to aphids, causes galls to form at the base of new shoots. It is difficult to prune out the galls without disfiguring the tree. Galls may also distract from the beauty and symmetry of the tree. If abundant, the galls may reduce the vitality of the tree and allow other insects to further weaken it.

Cooley Spruce Gall Adelgid: Galls caused by the Cooley spruce gall adelgid occur on Colorado blue spruce, Sitka spruce, and Engelmann spruce. The galls are somewhat larger than those caused by the Eastern spruce gall adelgid and occur on the tips of twigs. The growing gall varies from light green to dark purple. It may be 1” to 2” in length and ¼” to ½” in diameter. This insect most frequently infests blue spruce.

When it remains on the spruce, the life history of this adelgid is like that of the Eastern spruce gall adelgid. Some mature adelgids emerging from a gall in July or August fly to Douglas fir to lay eggs.

  • These eggs hatch into young adelgids which spend winter on the fir and produce a new brood in spring when growth appears.
  • These feed on new growth and cause distortion to the fir but do not form galls.
  • This adelgid does not need both hosts to complete its life cycle but is more serious when both hosts are present.

Do not grow Douglas fir and spruce together.


  • Needs to be treated during their dormancy
  • Prune out green galls in spring into early summer
  • Hire professional tree experts at Precision Tree for handling the damage done by adelgids!
  • Dormant oils are often applied in the Spring, and again in in late fall months
  • In mild infestations the brown galls can be picked off by hand – realize though the insects themselves are already gone.

Damage symptoms: Cone-shaped galls occur at the tips of the new growth of host plants. The galls turn brown in summer. Without intervention, at the very least, spruces will be disfigured and lose their distinctive shape, on the more damaging side, trees will be weakened as the same trees will be infested repeatedly, and other insects will also attack it. Strong winds or storms may easily take the trees down. Hiring the tree professionals of Precision Tree will help protect your trees.