The World of Entomopathogenic Fungi

A mycologist takes us into the strange world of insect- and other arthropod-infecting fungi, where nature’s tiniest organisms can do some truly mind-boggling things.

The fungal kingdom is vast and incredibly diverse. It is a kingdom that has helped shape life on Earth by decomposing organic matter, returning nutrients to the soil, and forming symbiotic relationships that help plants survive even in less fertile conditions. Fungi are the chemical masterminds of our ecosystems and, for those who take the time to notice, some of nature’s most fascinating storytellers. 

They are capable of remarkable things. They can create mutually beneficial relationships with other organisms, but they can also manipulate living hosts in ways that we may not yet fully understand. This is the story of a group of fungi that could turn the insect world into a living nightmare. Ghosts in disguise, they are called entomopathogenic fungi.

Illustration of Cordyceps militaris from Flora Batava by F. W. van Eeden (Leiden, 1889). Photo source: Wikimedia Commons.

Blackwellomcyes sp. found in Karnataka, with a wood-boring caterpillar as its host insect. Photo: Vhyom Bhatt

Cover image of an entomopathogenic fungus infecting a hornet (Vespa tropica).

Photo by Samuel John

The word entomopathogenic can be broken down into two parts: entomo, related to insects, and pathogenic, disease-causing. Together, it simply means fungi that infect and cause disease in insects. There are nearly 1,000 known species of entomopathogenic fungi described in scientific literature. Some of the better-known genera include Ophiocordyceps, Cordyceps, Isaria, Gibellula and Purpureocillium. Among them, perhaps the most famous is Ophiocordyceps sinensis, commonly known as Yarsagumba or the caterpillar fungus, which is wild-harvested from the higher elevations of the Himalayas.

• 

• 

• 

(1-3) Rising from the remains of an infected arthropod, these delicate stalk-like structures are the fungus’ route back into the environment. The projections consist of specialized spore-bearing structures - conidiophores, or groups of them fused into a synnemata. By elevating their reproductive surfaces above the host, the fungi increase the chances that the newly produced spores will be carried away and reach another susceptible host. Photos by Vhyom Bhatt.

But what makes these fungi so extraordinary is not just their diversity. It is the way they infect their hosts. These fungi do not need to be eaten by an insect. They simply need to make contact. When a fungal spore lands on the exoskeleton of an insect, the insect unknowingly allows a new organism to begin colonising its body. That single contact could eventually lead to a complete takeover of the host. 

The whole process is horrifying. Imagine an insect simply going about its day. It walks across a leaf or a piece of bark and unknowingly steps onto a fungal spore. The spore is roughly a thousand times smaller than one of the insect’s legs, so the insect has no idea that anything has happened. Under the right temperature and humidity, the spore germinates and firmly attaches itself to the insect’s outer body.

A spider in the family Salticidae infected with Gibellula sp., a highly specialised genus of araneopathogenic fungi whose known hosts are spiders. Although most species parasitise adult spiders, a rare species within the genus has been found to parasitise spider egg sacs instead. The fungus grows out of the spider’s body in distinctive stalk-like structures that release spores into the surrounding environment. Photo by Samuel John.

From there, the fungus begins producing enzymes that slowly break down the insect’s hard exoskeleton. Fine fungal threads, called hyphae, penetrate through this protective barrier and enter the insect’s body, where nutrients are plentiful. Once inside, the fungus begins to spread, feeding on the insect from within.

Different entomopathogenic fungi use different strategies. Some produce toxins that kill the insect before they fully invade the body. Others take a much slower approach. Instead of killing the insect immediately, they keep it alive while gradually consuming its internal tissues. The insect continues to walk, climb, and behave as if nothing is wrong, but the fungus is steadily taking control. In some species, the infection even alters the insect’s behaviour, guiding it to places that benefit the fungus rather than the insect. By the time the insect reaches its final destination, its body is no longer serving itself. It is serving the fungus.

So why does the fungus go through all this effort? The answer is simple: reproduction. Like many other fungi, entomopathogenic fungi eventually produce fruiting bodies that release spores. Those spores become the next generation, allowing the fungus to spread and survive.  To give those spores the best chance of success, the fungus needs the insect to die in exactly the right place. 

While controlling the insect’s movements, the fungus may direct it onto the bark of a tree, the underside of a leaf, or a branch higher up in the vegetation, where humidity and airflow are ideal. Once the insect reaches its destination, it dies. Over time, the fungus grows out through the body and produces its fruiting structures, releasing thousands of spores into the surrounding environment. What was once a living insect has now become the perfect platform for the fungus to reproduce.

Cordyceps: the fungus everyone knows

An ant infected by Ophiocordyceps spp., known for manipulating its host’s behaviour. Before dying, infected ants leave their nests and bite firmly into the underside of a leaf, a behaviour known as the “death grip.” As the infection progresses, the ant’s jaw muscles atrophy, helping lock its bite in place while the fungus grows and releases its spores. Photo by Samuel John.

Many of us may know the popular television series The Last of Us, which was inspired by a storyline where a fungus attacks, manipulates, and takes over the host bodies. This was inspired by the story of Cordyceps and its role in nature, particularly its relationship with insects and how it ensures its own existence. And just so you know, the fungus affecting humans is pure fiction.

Cordyceps is a genus of ascomycete fungi (they make spores inside tiny sac-like structures called asci) that has more than 260 species worldwide. Diverse species in this genus are used in Traditional Chinese Medicine for their properties. Cordyceps is now lab-grown in controlled environments to be used as a nutraceutical supplement, and the main molecular compound being researched is cordycepin, for its pharmacological effects.  Mushroom supplements have shown positive results in improving athletic performance, immune system modulation, heart health and anti-ageing properties. While this is the tip of the iceberg, there is a lot of potential hidden in entomopathogenic fungi that could be used as medicines. Several species are now being used as biological alternatives to chemical pesticides, helping farmers control agricultural pests in a more environmentally friendly way.

One story that brought Cordyceps into the spotlight dates back to 1993, when Chinese women distance runners broke multiple world records. When questions about doping arose, their coach claimed that the athletes’ performance was the result of intense training combined with Cordyceps supplementation. Whether Cordyceps actually played a significant role is still debated, but the story introduced the fungus to millions of people around the world.

Purpureocellium atypicola, a spider-associated fungus, has a rather complicated story. Long regarded as a single species, recent research suggests that it is actually a complex of genetically distinct fungi, each adapted to different spider hosts and habitats. Some grow directly from spiders living in webs, while others infect ground-dwelling or trapdoor spiders. Photo by Vhyom Bhatt.

Not all entomopathogenic fungi infect every insect they come across. Many are highly host-specific, meaning a particular fungus may infect only one species or a small group of closely related insects. Others have a much broader range of hosts. Of course, insects are not completely defenceless. Their immune systems can sometimes recognise and fight off fungal infections before they become established. Whether the insect survives depends on its own immunity, the strength of the fungus, and how far the infection has progressed. 

Entomopathogenic fungi help regulate insect populations and maintain ecological balance. Some species also live inside plants as endophytes, where they receive nutrients from the plant in exchange for improving drought tolerance, protecting against herbivorous insects, and enhancing disease resistance. Far from simply infecting insects, these fungi play multiple roles that support healthy ecosystems. 

As a biologist who studies and educates people about fungi, I believe there is still so much for us to understand about entomopathogenic fungi. They give us a glimpse into the incredible complexity of the fungal kingdom and the many ways fungi interact with the world around them. What may seem like a horror story to an insect is, from another perspective, an extraordinary part of nature. The more we learn about these fungi, the more we may discover ways to work with them and use their potential for the benefit of other carbon-based life forms.

---

About the author

Vhyom is a mycologist whose journey with fungi began in the Himalayas, where early experiences with foraging sparked a deep fascination. Over time, he expanded into cultivation and operations, working with gourmet and medicinal mushrooms. He now consults with mushroom startups, leads educational programs, and continues to explore the world of fungi through research and practice. A founding member of Mycovann, he sees fungi as wise, nurturing organisms essential to life’s interdependence.

Sharing is caring.

Share your thoughts with us in the comments section below.

Use the links below to share this story on your social networks.