Don't Let the Serpula Inside - A look at the crust fungus, Serpula himantioides
- Dec 1, 2025
- 5 min read
Good evening, friends,
This week we’ll look at a crust fungus that I learned about in Pelham Bay Park last weekend, and I was fortunate enough to reencounter today. As tends to be the case in both fungi and sandwiches, crusts are often overlooked and occasionally even discarded. Fortunately, on that walk in NYC we had a crust expert, Emma Richter of the Maine Mycological Association, to help us find these beautiful but seldom appreciated fungi.
This morning, I realized we had very similar conditions as we did on that walk in the Bronx: rain the prior evening and now it was cool and sunny. It seemed like the mushroom was fairly common so I figured I might as well see if I can find it on my own. I went to an area where I knew there would be dead conifers (Goodwill Park in Falmouth, MA) and within half an hour I had encountered Serpula himantioides for the second time.
Fun Facts
The fungus has a close relative, Serpula lacrymans, which is seldom found in the wild and more often found in the basement. The fungus has developed a taste for the wood beams of buildings and found a niche in the human-built environment. One study found that S. lacrymans, while a powerful digester of conifer wood, does not compete well with other fungi, and that is why it doesn’t grow nearly as prolifically in the wild. However, when it finds its way into your floorboards, it now has an open buffet. S. lacrymans has even been shown to digest wood that was treated with copper citrate and other copper-based wood preservatives used in pressure treated lumber (Reference 3).
Switching back to our fungus, S. himantioides has a hypnotic, brownish-gold, and wrinkled fertile surface surrounded by a white margin. A study out of Chile found that when exposed to UV-B radiation (sunlight), the fungus slows mycelial growth and instead uses its energy to create xerocomic acid, a compound that has photoprotective properties (a natural sunscreen) and is also antibacterial. The scientists suggest that the compound could eventually serve as a natural UV-protective ingredient in sunscreen and other cosmetics.
The fungus is in the Order Boletales which means it’s more closely related to the big, fluffy boletes (like the Foxy Bolete from a few weeks ago) and other fungi that form mycorrhizal relationships with plants, than to the shelf/bracket mushrooms (polypores) and other common wood decomposers with which it shares its log home. Interestingly, xerocomic acid is produced in other boletes, as well, and is one of the compounds responsible for the blueing reaction that occurs when some boletes are bruised/broken. There wasn’t any bruising on this mushroom, however.
Etymology
The genus name Serpula is derived from the Latin serpens which means “snake” and the suffix -ula makes it “little snake”. This refers to the snake-like movement of the crust as it slowly spreads, or slithers, its way down the dead log.
The species epithet himantioides was derived from the genus Himantia which seems to be a fungus with limited observations, so saying this is Himantia-like (which is what the -oides implies) doesn’t do too much for us. Himantia is derived from the Greek himántas which means “strap” or “thong”, like one you would find on a sandal. This could refer to the fungus’s capabilities to produce robust, mycelial cords that help it travel through hosts and digest wood, or it might just relate to the fact that the fungus produces a thin, strap-like fruiting body that can be peeled off the wood.
Ecology
The fungus is parasitic and causes a heart rot on living conifer trees (it digests the heartwood, the xylem cells in the middle of the tree). After the tree dies, the fungus continues to digest the wood and creates a brown rot. The fungus slowly eats the cellulose and hemicellulose in the plant cell walls, and the wood breaks down into brown, cubical, chalky chunks. Apparently, there are no signs the tree is infected with the fungus when the tree is alive, and fruiting bodies only grow on dead trees. The mushrooms also grow on decorticated wood, or wood that has already lost its bark.
The fungus I found today was on a large, dead Norway Spruce (Picea abies). While learning about this mushroom, I also learned that the “content of inhibitory extractives is greater in pine wood than spruce wood”, which means it’s easier for fungi to eat spruce rather than pine because the latter has more defense compounds in the wood (Reference 1).
The fungus has a global distribution and can be found on all six major continents in the cooler months, fruiting in the late fall and into winter. It seems to be found wherever spruce and fir trees are found. The fungus comprises a species complex with multiple, nearly identical fungi grouped under the name Serpula himantioides, and microscopy or DNA sequencing needs to be used to parse them apart.
Interestingly, there is actually one iNaturalist observation from Antarctica. This would be a first for a Mushroom Monday feature, something that can be found on every continent, but it doesn’t actually appear to be the mushroom. I’m not sure what it is, but it looks more like seaweed than anything fungal in my opinion. One of these days we’ll feature something you can find on all seven continents (likely it will be a lichen, but who knows)…
Puerto Rico and Other Upcoming Events
Our foray to Puerto Rico starts this Friday. Next Monday’s edition will be a feature on the mycologist Larry Millman, and the following Monday will feature a recap of the Puerto Rico excursion. I’m excited to see what we find and to share those findings with everyone.
Full moon on Thursday,
Aubrey
References
Balasundaram SV, Hess J, Durling MB, Moody SC, Thorbek L, Progida C, LaButti K, Aerts A, Barry K, Grigoriev IV, Boddy L, Högberg N, Kauserud H, Eastwood DC, Skrede I. The fungus that came in from the cold: dry rot’s pre-adapted ability to invade buildings. ISME J. 2018 Mar;12(3):791-801. doi: 10.1038/s41396-017-0006-8. Epub 2018 Jan 5. PMID: 29305577; PMCID: PMC5864223.
Torres S, González-Ramírez M, Gavilán J, Paz C, Palfner G, Arnold N, Fuentealba J, Becerra J, Pérez C, Cabrera-Pardo JR. Exposure to UV-B Radiation Leads to Increased Deposition of Cell Wall-Associated Xerocomic Acid in Cultures of Serpula himantioides. Appl Environ Microbiol. 2019 Aug 29;85(18):e00870-19. doi: 10.1128/AEM.00870-19. PMID: 31285193; PMCID: PMC6715839.
Tolerance of Serpula lacrymans to copper-based wood preservatives, 56, 0964-8305, http://dx.doi.org/10.1016/j.ibiod.2005.06.008, DOI=10.1016/j.ibiod.2005.06.008}, 3, International Biodeterioration & Biodegradation, Elsevier BV, Hastrup, Anne Christine Steenkjær and Green, Frederick and Clausen, Carol A. and Jensen, Bo, 2005, Oct, {173–177}
https://www.inaturalist.org/taxa/409595-Serpula-himantioides#map-tab