The Spooky World of Halloween Fungi

It is officially October and Halloween is just around the corner! When most people think about Halloween, they picture carved pumpkins, frightening costumes, and candy. But in nature, the season brings a different kind of transformation. Fall is the peak season for fungi, and some of the species that appear this time of year look like they belong in a horror film. Get ready to read about fungi that bring Halloween vibes!

Hydnellum peckii

This mycorrhizal fungus is native to North America and Europe, and has even been spotted more recently in South Korea. In the early stages of its growth, its white cap emits striking red droplets when moist, making it look like it bleeds. This explains the nicknames “Bleeding Tooth Fungus” or “Devil’s Tooth”. Less dramatic nicknames include “Strawberries and Cream” and “Red Juice Tooth”. These red droplets are a form of guttation or extracellular fluid, possibly as a way to get rid of excess moisture, though scientists are still trying to figure out what triggers it.

Under the cap, instead of gills or pores, you’ll find tiny tooth-like spines. This is a characteristic feature of the genus Hydnellum. These spines carry the developing spores. Alongside its bizarre appearance, this fungus also stands out with its chemical properties. It produces a pigment called atromentin, which has anticoagulant and antibacterial properties. Hydnellum peckii is technically not toxic, but is considered inedible due to its bitter taste.

Xylaria polymorpha (Dead Man’s Fingers):

This saprotrophic fungus is pretty common in forests across North America and Europe. It typically grows at the base of decaying hardwood stumps or buried roots and produces upright fruiting bodies which emerge in small clusters. The cluster’s irregular, twisted shape look a lot like decaying fingers, which is how it got its creepy nickname Dead Man’s Fingers. When young, it’s often bluish with a white tip coated in asexual spores (called conidia). The white tip disappears over time as the fungus matures, and the fungus switches to sexual production.

The inside of the fungus is white and fibrous, while the outside eventually turns rough and develops tiny black openings called ostioles, which help release spores. The fungus often stays for months or even years above ground, slowly spreading spores the whole time. Just like Hydnellum peckii, Xylaria polymorpha is inedible but not toxic. 

Xylaria polymorpha plays an important role in forests by breaking down lignoncellulose in dead wood. This process returns nutrients like carbon, nitrogen, and minerals back to the soil, and make them available for plants and other organisms. Studies have also found that X. polymorpha is a unique source of laccase enzyme capable of breaking down pharmaceutical pollutants like amoxicillin in wastewater. In fact, laccase derived from this fungus works even better than many commercial versions, which makes it a promising, eco-friendly option for bioremediation.

X. polymorpha is also known to produce melanin in its fruiting body, which gives it a distinctive dark color. Specifically, it makes a type called DHN-melanin, which helps protect the fungus from UV radiation, oxidative damage, and drying out. Melanin also helps in the fungus’s wood-decay work by making the black zone lines you see in spalting, which act like boundary markers to keep other fungi out. Because of its biochemical resilience and pigment properties, melanin from X. polymorpha is gaining attention for potential use in biotechnological applications, such as natural antioxidants, protective coatings, and bio-based materials. 

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Clathrus archeri (Devil’s Fingers):

This fungus is among the most unusual looking fungi out there. While it is native to Australia and Tasmania, you can now find it in Europe, North America, and Asia as well. The fungus starts its lifecycle as a soft, white egg-looking structure. As it matures, the egg rapidly bursts to reveal four to eight bright red, finger-like arms that curl outward. The shape has reminded many people of octopus tentacles, which led to the nickname “Octopus Stinkhorn.”

The reason it’s characterized as a stinkhorn is its unpleasant odor. Its bright red arms are covered with a foul-smelling, dark green slime known as “gleba” on the inner side, which contains the fungus’s reproductive spores. The foul smell is of course not a coincidence: it attracts carrion lover insects, which inadvertently carry the spores away and help disperse them. 

The red color of the arms comes from carotenoid-like compounds, and their structure is supported by fungal hyphae packed with air chambers, which let them expand quickly once they emerge. The whole process of emergence can take just a few hours, making it one of the more dramatic fungal appearances in nature.

There are no known medicinal or culinary uses of this fungus. But, it has drawn interest in chemical ecology, especially for understanding how decomposer fungi mimic the chemical cues of decaying animals.

Gyromitra esculenta (Brain fungus):

This saprotrophic fungus fruits from late spring to early summer. Despite not fruiting around Halloween, its wrinkled, brain-like, brown cap has given it a somewhat unsettling reputation, much like other fungi mentioned above that tend to appear around Halloween. This unusual cap is what earned it the nickname “brain fungus”. It’s also called a false morel, because it’s often mistaken for true morels Morchella spp. This confusion can be deadly, since true morels are edible, whereas Gyromitra esculenta are toxic. Specifically, it contains the toxin gyromitrin, which breaks down into monomethylhydrazine (a common volatile used in the production of rocket fuels). Eating this toxin can cause severe liver damage, seizures or even death.  

Surprisingly, in Finland, this fungus is considered conditionally edible, meaning that it is edible only when it is prepared in a very specific way to reduce toxicity. Monomethylhydrazine is a heat-sensitive and water-soluble compound, so it can be removed through careful preparation. Over time, it’s become part of Finland’s food culture and even shows up in dishes like false morel stew (huhtasienimuhennos). Still, health officials strongly advise against eating it, just to be safe.

Auricularia auricula-judae

Often called “wood ear” or “jelly ear”, this fungus is easy to recognize thanks to its shape that looks like ears and its rubbery texture. Its color ranges from brown to dark purplish-black, and it usually grows on decaying hardwood trees. As a saprotroph, it feeds by breaking down dead organic matter.

Scientific studies, especially in vitro and in animal models, have found that wood ear has a range of potential health benefits, from antioxidant, antidiabetic, and anti-obesity effects to anti-inflammatory, anticancer, antimicrobial, and anticoagulant activities. It may also boost gut health by supporting good bacteria like Bifidobacteria. Aside from its medical use, this fungus has earned an important spot in East Asian cuisine, and is often used in stirs and soups. Though it looks eerie when moist, Auricularia auricula-judae is anything but sinister. 

Tremella mesenterica (witch’s butter)

This striking fungus is known for its golden-yellow, lobed fruiting body. Similar to the wood ear, it has a gelatinous fruiting body that gets slimy and greasy when damp. Tremella mesenterica is not a typical saprotroph or mycorrhizal fungus; instead, it is a mycoparasite and infects other fungi, particularly Peniophora species. It uses specialized hyphae to invade the host fungus and extract nutrients. 

Tremella mesenterica produces glucotonoxylomannan (GXM), which is a capsular polysaccharide that contributes to both its gelatinous structure and medicinal properties. Made up of mannose, xylose, and glucuronic acid, GXM is produced in large amounts in both the fruiting body and the cultured mycelium. It helps the fungus hold onto moisture and avoid drying out, which is what gives it that signature gelatinous look. More importantly, GXM has been shown to exhibit immunomodulatory, antidiabetic, and anti-inflammatory properties, making it of growing interest in pharmaceutical and nutraceutical research.

As the example above show, while these fungi are known for their unusual (sometimes even unsetting) appearance, many are also highly valued for their culinary and medicinal benefits.

Let me know in the comments if you know any other bizarre, eerie, or spooky fungi!