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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


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


Sung to the tune of Rudolph the Red-Nosed Reindeer. If you forgot the tune, or never knew it, just visit the following web site:

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.

We've met aphids and whiteflies,
And leaf notching weevils;
Stink bugs and bed bugs,
We know all their evils.

But what do I see
All over my Christmas tree?

Cooley spruce gall adelgids
Decorate my fine fir tree;
Lots of waxy white balls
Full of small bug eggs for me!

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

Later on in the spring time
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 into 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.

These curious suckers moved east from the Colorado Rocky Mountains along with their host trees, Douglas fir and various species of spruces. 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 pass a second generation on fir before migrating to spruce trees like Colorado blue spruce. On spruces they form curious, pineapple shaped galls at the terminals of branches. From these galls emerge migrants that return to Douglas fir to complete the complex and bizarre life cycle. What fun it is to find a beautiful Douglas fir already decorated with adelgids for Christmas!


Our apologies to Gene Autry, who recorded this 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 web sites: