A Practical Joke?

The road led into a small forests. The trees next to the road showed a remarkable yellow to brown fungus. Very different kind of trees, both dicots and gymnosperms. I stopped, and took photos:
The fungus feeled very hard, rather like plastics - but such fungi often feel not natural either. Only trees close to the road seemed infected, no one farther into the forest. And only on the lower part of the trees…
Well, some other iNaturalist thinks that it resembles isolation foam, and someone sprayed the trees with it.
He may be right.
But who tf is out there in nowhere tricking iNaturalists - a place where hardly any observations have been made yet?
Has something similar also happened to you?


How frustrating. I can’t say I’ve seen anybody deliberately trying to mislead naturalists. I have gotten rather excited about something that I’ve seen quickly and then upon closer inspection realized was manmade. I can’t say I’m thrilled that someone would think spraying insulation foam on trees a great joke–seems very careless and disrespectful to the environment. I hope it doesn’t continue.

I did find this in a Google search:
“If the tree hole holds water, fll the tree hole with expanding foam used for
home insulation projects. Look for a product that is made to fll big gaps
and is water resistant. Follow directions on the product label.
• Expandable foam is light weight, seals the hole, and keeps it from collecting
water, and is fexible enough to move with the tree.
• You do not need to clean out the tree hole before filling.”

It’s for mosquito control apparently, but why that would happen in the middle of nowhere, I don’t know.


This kind of foam is normally used to fill tree cavities:

  • This paper recommends it to keep feral bees out of tree cavities
  • This website suggests it as a way to keep kids out of tree cavities (there’s more information, but that’s the most important use-case, obviously!)
  • This observation by @neontetraploid shows typical use case

It’s often sold in cans, like spray paint with a popular brand called Great Stuff. Maybe this is a case of whomever was filling in tree cavities either testing their can of spray foam or discharging leftover foam from a nearly empty can?

Edit: For your observation, it’s almost like they’re misapplying it as weed killer or maybe hoping it’ll prevent a broken tree crotch? They’re applying it over and over again maybe to prevent plants, etc. from sprouting/ocuppying? So strange!


Oh yeah, that’s definitely insulation foam.The amount of times I’ve been tricked into thinking it was Laetiporus sulphureus driving by globs on the roadside is a non-zero number


Surely not done for mosquito control, as no holes in the tree were filled - the foam is just sprayed onto the tree.

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H-m-m-m. Then, maybe a teenager with a can of the stuff and nothing to do? (I say teenager because I’ve seen my own students do odd things just because they’re bored, but it certainly could be an adult.) It’s weird. I hope it’s not some new trend whereby a person defaces nature just to let others know they were there.

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Like people scratching shit into beech & aspen bark? Or cave walls? People have unfortunately been defacing nature for longer than any of us have been alive


The fact that it happened at least 3 times is worrying. It implies that it’s someone’s tradition, so maybe worth revisiting in a year or so, just to check?

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This stuff or something similar is also used in closure projects for abandoned mines, the closure being for human safety reasons. I think they bring it in by the barrel to close smaller adits. Usually an assessment of wildlife use is done first.


I’ve used that, but only in our own yard. Flowering crabapple with a bad case of carpenter ants. Followed them and could see where they were coming and going from. Squirt squirt. The tree recovered, thrived, and no more ants.

But for use in the wild? I have no idea.


Well, true. Hadn’t thought about that. I just happen to like cave paintings. :) I find spray foam less aesthetically pleasing, but it is the same principle.

I find spray foam back on the woods, just in clumps on the ground, far away from creeks, and not too close to houses. Thought it was slime mold at first.


According to Dupont: “Prior to spraying the foam, surfaces must be dry, firm, clean
and free of dust, grease or loose particles”

I doubt this advice is followed when being used in a tree cavity, thus allowing moisture to get under it where it will take longer to dry out.

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