Slime WHAT? I’m flux-moxed!

I knew the headline would be catchy! I was indeed flummoxed (or greatly bewildered) when I saw the foam blobs on our Douglas fir trees today after the rain subsided enough for me to walk around outside. We’ve had a DELUGE of rain in the Pacific Northwest this year. Rumor has it, the rain is record-setting!

Back to the giant spit-wad looking blobs of bubbles on those trees…. Here’s what I saw.

Pseudotsuga menziesii Douglas fir trunk with foam blob

I’m an entomologist, so when I saw this I thought, “it sure looks a lot like the foamy froth that spittle bugs make.” However, I quickly discounted this possibility (unless there was some sort of really LARGE undiscovered species hiding out on San Juan Island that is) because it’s way too early in the season for them.

What WOULD we do without Google? Seriously! I typed in a search. My first query was “what do Pacific tree frog eggs look like?” I was skeptical, but since I heard tree frogs around me in the woods and since it is REALLY wet outside, I thought maybe one or two of these frogs got confused and used the tree instead of one of the thousands of water puddles I was trying to avoid stepping in. Nope. Not tree frogs. My next query read like this…”weird, foam mass on Douglas fir tree trunk.” I got a few things, but quickly narrowed the possibility to the sites that had photos that looked like mine.

I discovered these oozing foamy spots are called SLIME FLUX, also known as a condition of the tree called WETWOOD. Sounds bad. Might be.

I’ve not had a chance to read through all of this material. It sure seems like there is a link between harmful bacteria, water, possibly insects, and the resulting foam. but will share it here for you to reference.

While scanning this document, the term that popped out at me was “slime-flux insects” on page 8. I’ll have to do some more reading to investigate this. If you beat me to it, please feel free to share your comments. Curious minds want to know!


I’ve been doing a bit more reading about slime flux and foamy trees this evening (check out this site and found an alternative and possibly more probable cause. While the foam can be caused by bacterial infections, it also is known to form after periods of heavy rain when a chemical reaction of sorts occurs. The rain interacts with soap-like components found in the sap from pine trees (and probably this includes fir trees as well), creating foam similar to what I observed today. It can also form from air pollutants that land on the trees after dry periods and create foam when rain hits the tree bark.

Fi Fi Fo Foam! I learned the best way to tell the difference between friend or foe foam is to take a whiff. Bacterial infections produce a foul-smelling foam that bubbles out as tree tissue is broken down, forming alcohol and carbon dioxide gas. This foam will often attract insects like bees, flies, wasps, and ants.

The most-detailed explanation about what happens during this process I found on the Penn State Extension Website, and I’ve copied below from their site (found here ~

“Bacteria, commonly found in soil and water, take up residence in young trees or gain entrance to older trees through wounds. The bacteria, including species of Clostridium, Bacillus, Enterobacter, Klebsiella, and Pseudomonas, grow within the tree using the sap as a nutrient source. As the sap is used, oxygen in the heartwood is depleted (creating anaerobic conditions), methane is produced, the pH of the sap is increased (pH 6 in healthy trees to pH 7 to 8 in wetwood), and a high pressure develops in the wood (60 psi in affected trees vs. 5-10 psi in wetwood-free trees). The resulting environment greatly inhibits the growth of fungi that can cause interior rots. The liquid kills grass and other herbaceous plants that it contacts at the base of the tree. The wood of affected trees has greatly reduced value as lumber because of the unsightly discoloration. Affected wood dries much more slowly than wood taken from wetwood-free trees.”

Another good page to check out if you want to read more about slime flux or Wetwood is found at ~

P.S. Post YOUR best slime flux photos here! Thanks for reading.

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