Flesh-Eating Fungi: A Guide to Carnivorous Mushrooms

If you usually view fungi as idle, unassuming organisms, we don’t blame you. For the most part, fungi are indeed low-key and often go unnoticed, but some species can be quite aggressive, maybe not to humans but to other microbes and small insects around them. Carnivorous fungi aren’t your typical passive decomposers. These unique fungi have evolved some unorthodox strategies to obtain nutrients beyond their usual decomposer diet, trapping and consuming live organisms for their own survival. Even some of your favorite edible mushrooms might not be as innocent as you think, which just goes to show that fungi can be more complex than most give them credit for. So the next time you stumble across a stray mushroom in the forest, remember that it could have a more sinister side lurking beneath its seemingly harmless appearance.

Why are some fungi carnivorous?

Fungi are saprotrophic organisms, meaning they don’t have the ability to produce their own food through photosynthesis like plants do. Instead, they must rely on decomposing organic matter for their sustenance. To do so, fungi secrete specialized enzymes that can break down complex organic materials so that they can absorb the nutrients they need. While the majority of fungi strictly rely on this method to obtain their nutrition, some species have evolved to capture and consume small organisms like nematodes and single-celled eukaryotes called protozoa.

But why have certain fungi developed these carnivorous tendencies? Researchers believe these traits may have been established as an adaptative response to environmental pressures (1). Fungi that live in nutrient-poor environments might have started capturing prey as a way to supplement their diet and ensure their survival. This trait especially comes in handy when there is not enough nitrogen in the soil, which fungi require for protein synthesis and other necessary cellular functions. By preying on other organisms, these fungi can continue growing and reproducing in conditions that would otherwise be considered inhospitable.

Feeding mechanisms of carnivorous fungi

Bob Blaylock via Wikimedia Commons

You may be wondering how fungi can catch and consume other organisms, considering they don’t have any hands, teeth, or mouths. Since most fungi are strict decomposers, they break down matter using a thread-like network called hyphae, which secrete digestive enzymes and absorb nutrients. Carnivorous fungi still have this capability; however, they also use their hyphae to attract and capture unsuspecting victims for their next meal. Once the prey is caught, carnivorous fungi use their hyphae to wrap around and penetrate the organism, then secrete enzymes directly into them to break down their tissues. There are several different methods that carnivorous fungi have evolved to capture their prey, including:

• Sticky traps like adhesive networks, knobs, and branches are attached to hyphae and coated with a sticky substance to catch any organisms that come into contact with them.
• Constriction rings are ring-shaped structures positioned along the fungus’s hyphae that tighten around their prey once they come into contact. When an organism goes through the ring, the cells inflate and constrict around it to trap and prevent it from escaping.
• Endoparasytism is a more insidious method of capturing prey because, this time, the organism doesn’t even need to cross paths with a fungus to be infected. Instead, the fungus creates spores that are designed to directly infect their host organism through ingestion or bodily contact. After the spores reach the inside of the host’s body, they germinate and develop hyphae, which spread throughout the host while consuming its internal tissues. By internally invading their prey, the fungus can absorb nutrients directly from within the host, leading to a slow yet eventual death.
• Toxin secretion is a method used by some fungi to immobilize or kill their prey. These toxins, produced on the surface of the fungus’s hyphae, disrupt the cellular functions of an organism once it comes into contact, eventually leading to paralysis and death.

Types of carnivorous fungi

There are over 200 different species of carnivorous fungi, from microscopic assassins to well-known edible varieties that might surprise you with their predatory abilities. Some of the more notable carnivorous fungi include:

Arthrobotrys spp.

Bob Blaylock via Wikimedia Commons

Arthrobotrys fungi are well known for their capacity to create complicated sticky networks that catch nematodes. These fungi usually appear in soil and decomposing organic debris, where they help regulate nematode numbers. Because of their complex trapping processes, they are an important subject of study for understanding fungal predation.

Oyster mushrooms (Pleurotus ostreatus)

Oyster mushrooms are a widely consumed culinary favorite, yet they have a darker side that many are unaware of. These fungi thrive on decaying wood and plant matter, but they also love to delight in a hearty meal of nematodes whenever they get the chance. But don’t let their uncanny diet deter you from enjoying these delicious and versatile mushrooms.

Cordyceps militaris

Another popular mushroom, celebrated for its medicinal abilities, cordyceps, is also known for its predatory behavior towards insects like caterpillars, ants, spiders, and locusts. This freaky fungus inspired the skin-crawling video game and eventually the TV series “The Last of Us,” but don’t worry, these mushrooms are not known to pose any threat to humans. Despite its creepy reputation, this mushroom is actually considered safe for consumption and has a wide range of proposed health benefits, including enhanced energy, immune support, and inflammation management.

Hirsutella spp.

Bugwood.org via Wikimedia Commons

Many fungi from the Hirsutella species are fungi notable for their parasitic lifestyle, which mainly targets nematodes. This fungus, which is mostly found in soil, is an important natural regulator of nematode populations. It is currently the subject of ecological and agricultural research because of its distinct parasitic style and effectiveness in reducing nematode populations.

Scientific applications

Although carnivorous fungi may sound a tad bit threatening, they actually have several intriguing applications in science. Researchers have been exploring the use of some of these fungi as a means to control pest populations in agricultural settings, which could reduce the need for chemical pesticides. For instance, oyster mushrooms are experts in capturing nematodes. These parasitic worms can feed on the roots, stems, and leaves of crops, causing severe damage, reducing yields, and transmission of diseases. Studies have found that oyster mushrooms are rather effective at reducing nematode infestations, and if scientists can figure out how to use this solution on a widespread scale, it could revolutionize pest control in agriculture. Instead of using pesticides that can cause harm to birds, fish, humans, and beneficial insects, oyster mushrooms may hold the key to a targeted treatment that only impacts nematodes. Several other parasitic fungi have similar capacities and are also being examined for their pesticidal potential, including Hirsutella rhossiliensis, which targets nematodes by attaching to and penetrating their cuticles, and Duddingtonia flagrans, which uses sticky hyphal traps to ensnare and digest nematodes. Additionally, cordyceps are being studied for their biocontrol potential in protecting against insects and plant pathogens (2).

Scientists have also been looking into the potential of proteins like pleutolysin from oyster mushrooms to develop new medical treatments. Oyster mushrooms use pleurotolysin to break down their food, rupturing their cell membranes and facilitating easier absorption of nutrients. The compound’s ability to form pores in cell membranes could be harnessed for targeting and destroying harmful cells, such as cancer cells, or for fighting bacterial infections (3).

Fungi are full of surprises, especially the carnivorous kind. These extraordinary creatures demonstrate the cleverness of nature, transitioning from humble decomposers to fierce predators in their pursuit of survival. Their special adaptations illustrate life’s shocking diversity and hold promise for groundbreaking applications in science and agriculture. Whether controlling pests naturally or inspiring new medical treatments, carnivorous fungi remind us that even the smallest players in the ecosystem can have a big impact.

References

1. Lukoyanova, Natalya, S.C Kondos, Irene Farabella, Ruby H.P. Law, Cyril Reboul, Tom T. Caradoc-Davies, Bradley A Spicer, et al. 2015. “Conformational Changes during Pore Formation by the Perforin-Related Protein Pleurotolysin.” PLOS Biology 13 (2): e1002049–49. https://doi.org/10.1371/journal.pbio.1002049.
2. S., Saranya, and Priya John. 2021. “Cordyceps Militaris: An Emerging Biological Tool in Crop Protection.”
3. Yang, Ence, Lingling Xu, Ying Yang, Xinyu Zhang, Meichun Xiang, Chengshu Wang, Zhiqiang An, and Xingzhong Liu. 2012. “Origin and Evolution of Carnivorism in the Ascomycota (Fungi).” Proceedings of the National Academy of Sciences 109 (27): 10960–65. https://doi.org/10.1073/pnas.1120915109.