Name: Adelges cooleyi

Alias: Cooley spruce gall adelgid, or wooly aphid. The gall adelgid gets its first alias from its ability to make large galls on spruce trees, and it gets its second alias because it is a small insect similar to an aphid and it often appears to have wool or cotton coming off its back. It is sometimes mistaken for cotton cushony scale, but the difference is that it is mobile and specifically targets Colorado spruce (blue spruce) and Douglas fir trees. Other than wooly, it can also appear to be brown, gray or tan with no wool. It is very rare to see the insect itself. They are quite shy and their presence is mostly noted from the damage they cause. The females take a year to mature and by spring they lay hundreds of eggs at the tips of new growth where they can soon feed.

Crimes: The spruce gall Adelgid is an expert at feeding on the tips of spruce and fir trees, leaving a large unsightly swollen gall that is green in early spring and by summer it resembles a pine cone. They use this large gall as protection from would-be predators. While this is a benefit for them, it leaves brown tips across the tree. This is the most obvious way to know of gall adelgids are present.

Redeeming qualities: None known.

Sentence: There is no need to control Cooley spruce gall adelgid populations. The damage they cause is purely aesthetic and causes very little stress for the tree. These galls can be trimmed off if they cause unsightly damage.

For more information on dangerous and beneficial bugs, call UI Extension educator Joseph Sagers at 208-270-4031 or email

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