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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Cooley spruce gall adelgids, Adelges cooleyi, decorate the Christmas tree


On Douglas fir, female Cooley spruce gall adelgids lay dozens of eggs in cottony masses of wax. Eggs hatch and small brown nymphs settle down to feed.


For many folks, one of the best traditions of the holiday season is the annual visit to the Christmas tree farm to choose and cut an evergreen to enliven the home. Douglas firs are one of my favorites, and a few years ago I was fortunate to find one loaded with a fine collection of white, fluffy egg sacs courtesy of the Cooley spruce gall adelgid. These curious suckers moved to the eastern United States from the Colorado Rocky Mountains along with their host trees, Douglas fir and various species of spruces.

Cooley spruce gall adelgids enslave the genetic machinery of the spruce tree, causing it to form an abnormal, pineapple-shaped home for the insect, called a gall.

On Douglas fir, female adelgids make white, cottony masses of wax in which dozens of eggs will be laid. From these eggs hatch nymphs that insert tiny beaks into the fir tree where they obtain nutrients and will pass a second generation before migrating to spruce trees, including Colorado blue spruce. After passing the winter on spruce, with the arrival of spring they tap into new shoots with their beaks and secrete potent growth regulators that enslave the developing spring growth and command it to form curious, pineapple shaped galls at the terminals of branches.

Within the gall are dozens of chambers housing spruce gall adelgid nymphs.

From these galls emerge winged migrants that return to Douglas fir to complete their complex and bizarre life cycle. One way to manage these insects in Christmas tree plantations and landscapes is to avoid planting Douglas firs and spruces in close proximity. But for bug geeks, what fun it is to find a beautiful Douglas fir already decorated with adelgids for Christmas!    



To celebrate the adelgid and get into the holiday spirit, why not sing a verse or two of the Cooley spruce adelgid song? It’s sung to the tune of Rudolph the Red-Nosed Reindeer.  If you forgot the tune, or never knew it, just click on this link and sing along with the Bug Guy.


Cooley spruce gall adelgid

We’ve met aphids, and whiteflies,

And leaf notching weevils,

Stink bugs, and bed bugs,

We all know their evils.

But what do I see

All over my Christmas tree?


Cooley spruce gall adelgids

Decorate my fine fir tree,

Lots of white balls of waxes

Full of small bug eggs for me!


Later on in the springtime

When warm breezes start to blow

Hundreds of eggs will have hatched

Into tiny nymphs, you know.


Nymphs will take their small sharp beaks

And jab them in the tree;

Sucking sap is what they do -

Glad they don’t suck me or you!


Then they turn into adults

And develop wings and fly

To Colorado spruce trees

That are growing right nearby.



Three wise Brood II cicadas wish everyone a Happy Holiday season and joyous New Year.



Our apologies to Gene Autry, who recorded a version of Rudolph the Red-Nosed Reindeer composed by Johnny Marks in 1949. The interesting article “Phylogeography of a specialist insect, Adelges cooleyi (Hemiptera: Adelgidae): historical and contemporary processes shape the distribution of population genetic variation” by Robert G. Ahern, David J. Hawthorne, and Michael J. Raupp was used as a resource for this episode.

To learn more about the Cooley spruce gall adelgid, please visit the following website: