Introduction
Cordyceps fungi have long fascinated scientists and the public alike due to their remarkable ability to hijack the bodies and minds of their insect hosts. While these parasitic fungi have been known in biology for centuries, many people may have first heard of it through the hit show The Last of Us, which imagines a world where a mutated Cordyceps strain infects humans, leading to a global pandemic. Though fictional in that context, the real-life Cordyceps fungi exhibit behaviours that are no less astonishing.
As science writer Isabella Backman describes, “The spores of the Cordyceps seize control of the mind and motor functions of their host, causing erratic behaviours and spurring the insect to seek a higher location 1” This dramatic process showcases the eerie precision with which Cordyceps manipulate their hosts, ensuring their own survival and proliferation.
Beyond their macabre life cycle, Cordyceps fungi have gained attention for their medicinal properties and economic importance, with species like Ophiocordyceps sinensis being highly prized in traditional medicine.
This article explores the biology, morphology, life cycle, and broader significance of the fungi, shedding light on one of nature’s most intriguing parasites.
Habitat And Distribution
Ophiocordyceps or cordyceps is a specialised parasite that infects, manipulates and kills formicine ants. Cordyceps is predominantly found in tropical ecosystems, and its distribution includes the Brazilian Amazon, Thailand as well as Japan 2. This is because the tropical conditions provide an ideal environment for fungi to survive. For example the high moisture levels are provided by tropical rainforests ,which on average have rainfall of 2,000 to 10,000 millimetres per year, 3 which is extremely important to fungi as they absorb water through their cell walls as they do not have a specialised system to transport water such as the xylem in plants and this water is then used for various metabolic processes in fungi themselves. As well as the high moisture levels there are also moderate stable temperatures nearly all year round, with the average temperature in tropical rainforests being 25 degrees Celsius,4 which is important for fungi as the optimum temperature for enzyme activity will be around 30 degrees Celsius thus promoting growth. Along with many other factors, this means that tropical environments provide an almost perfect environment for cordyceps to survive in.
Life Cycle and Parasitic Nature
Cordyceps is a parasitic fungus which means that it is an organism that lives in another species (its host) and benefits by deriving nutrients at the other’s expense 5. The host for cordyceps are ants, more specifically formicine ants which include the common carpenter ants 6.
The life cycle of cordyceps is extremely interesting, and includes several different processes which are spore attachment, host invasion, internal fungal growth, behavioural manipulation (giving the ants their zombie-like characteristics), fruiting development and finally spore dispersal.
Host Invasion
Cordyceps reproduce both asexually and sexually through spores (the asexual spores are referred to as conidia and the sexual spores as acrospores) and these spores are released into the environment from a fruiting body which in most cases is that of a dead arthropod. These spores like other fungi are dispersed by wind, water or contact with other animals. These spores, if they land on a suitable host which in many cases is an ant, attach to the cuticle of the ant which makes up its exoskeleton 7. The cuticle of an ant is a composite material that consists of arrangements of highly crystalline nano-fibres embedded in a matrix of proteins 8. And the cuticle acts as a physical or chemical barrier protecting the insect from damage 9 and this is facilitated by the chitin because it forms microfibrils that are stronger weight for weight than bone or steal 10. The spore once it has landed on the cuticle then attaches to the exoskeleton using hydrophobic proteins and other adhesive molecules, this is an extremely important stage because without these molecules the spore would not adhere to the exoskeleton and be able to resist being washed away or insect grooming 11. Examples of the proteins and adhesive molecules that are used by cordyceps are mannoproteins which are glycoproteins that have a hydrophobic region and contribute to the adhesion to the exoskeleton of the arthropod by interacting with the chitin present in it, hydrophobins which are surface active proteins that help the adhesion by forming a hydrophobic coat 12, and lectins which are carbohydrate binding proteins that recognise specific sugars that are present in the cuticle helping adhesion and attachment 13.
Internal Fungal Growth
Once attached to the cuticle, the spore will germinate and hyphae are produced (which are the feathery filaments that make up the multicellular fungi), hydrolysis enzymes such as chitinases, proteases and lipases then break down the exoskeleton of the insect which is extremely impressive due to the strength of it as detailed earlier 14. Once these hyphae have penetrated the host’s body cordyceps will then begin to develop into a network of mycelium (which is the vegetative part of the fungus that is made of the white filaments 15), which spreads through the tissue that are present in the ant. The mycelium will grow by absorbing the nutrients that are present in the insect’s haemolymph (which is a fluid that is similar to the blood that is present in vertebrates and circulated through the interior of the invertebrate’s body, in contact with the tissue that is present in it transferring the nutrients to it by simple processes such as diffuses 16), fat reserves as well as the internal organs present in order for the mycelium to grow more 17.
Manipulation of Host behaviour
We will now look at the most interesting part of the behaviour of cordyceps which is the manipulation of its host (however, this process does not happen in all species of cordyceps), which gives Ophiocordyceps its name the zombie fungus. To manipulate the hoist the Ophiocordyceps then releases neuromodulating chemicals which can affect the host’s nervous system resulting in the fungi taking complete control of the ant 18. Specific examples of the chemicals that are released are Sphingosine 19 which is known to be extremely involved in several neurological processes so by secreting this chemical as well as Guanidinobutryric Acid 20 cordyceps effectively gains control of the ant and the ant in its zombie state succumbs to doing the actions of the fungi, forcing it to leave their colony and climb to a specific height along the vegetation that is present (which is often 25cm) as at this height it is hotter and more light will fall than down below (providing an almost perfect environment for the growth of the fungi and cordyceps), the ant will then bite onto the plant in its last act which is often referred to as a “death grip” where it will then lock itself into place, and the host will eventually die due to the breakdown of its tissue as well as because of the presence of fungal toxins 21, 22.
Fruiting Development, spore dispersal and reproduction
Once the host has died the mycelium that is present inside it continues to develop and will eventually consume all the internal organs. After a period of time, a stroma will emerge from the host’s body bursting through its exoskeleton 23, which may have inspired the unnatural appendages that are present on the zombies during their latter stages in the Last Of Us. The stroma is a specialised system that forms new spores for asexual and sexual reproduction which have both been discussed previously. Once the stroma matures it will then release millions of spores into the air and these spores will similarly land on an unfortunate insect and the cycle will start again.
Morphology and Structure
As described previously there are three main parts of cordyceps, these are the mycelium (the thread like network which grows through the tissue of the host and retrieves nutrients for the growth of the network), the fruiting body which is normally club-shaped or elongated and emerges from the body of the insects and lastly the spores.
Mycelium
Provided below is a picture of the network that the mycelium of cordyceps unilaterilis forms in an insect that has been able to emerge from the body of the insect after it has died.
JellyBean49 Getty Images
Fruiting body
The fruiting body that is present in cordyceps shows some variation from species to species, but specifically in cordyceps unilateralis the fruiting body produces a single slender fruiting body that often emerges from the neck of an ant. The stroma which has perithecia which are involved In the production of the sexual spores in cordyceps can also be observed just below the tip of the stroma that is present 24, and this is clearly shown in the image that is provided below.
Katja Schulz / Flickr
Spores
The spores that are produced form the fruiting body of the fungi have already been discussed in depth in terms of the chemicals that they product previously, however what we haven’t discussed is that cordyceps belongs to a a group of Asomycata which means that the spores that cordyceps produces are inside structures that are known as asci and this structure is shown in the image below 25.
David P. Hughes, Maj-Britt Pontoppidan
Impact On The World Today
Unlike cordyceps portrayal in the Last Of Us where due to global warming, a mutated strain of cordyceps that has adjusted to be able to survive at higher temperatures and this in the body of humans, takes over the world causing a zombie outbreak. This is highly unlikely to happen in reality this is because the jump from insects to humans makes this event highly improbable, as well as the fact that there are millions of fungi around the world that when human’s have been exposed to don’t cause infections and therefore, realistically cordyceps isn’t going to cause any zombified humans any time soon. However, despite this, Cordyceps has several impacts on the world today, for example some Cordyceps species for example Cordyceps Sinesis are extremely important in some traditional Chinese medicines and modern pharmacology (which if you didn’t know plants and fungi make up a large proportion of new drugs that have been discovered).
Benefits of Cordyceps in medicine
It boosts the immune system and helps to support it as it boosts macrophage and T cell activity 26. Where macrophages are a type of white blood cell that can surround and kill microorganisms through a process that is known as phagocytosis 27 and T cells which are involved in the protection of the body against infection and cancer 28.
Cordyceps can also provide energy and stamina enhancement and many athletes today use cordyceps, where in 1993 for example many Chinese female runners broke records in the long distance events including the (1500m, 3000m and 10,000m events). And afterwards, their coach came out and proclaimed that their success was due to a diet which contained cordyceps and heralded that it was due to their antioxidant effects which helped to improve their capacity to exercise 29.
Conclusion
Cordyceps fungi are remarkable parasites that exhibit complex life cycles, intricate host manipulation, and highly specialised morphological adaptations. From their ability to invade and control insect hosts to the development of striking fruiting bodies, these fungi represent one of nature’s most fascinating biological phenomena. Beyond their ecological role, Cordyceps species have garnered significant interest for their medicinal properties, particularly in traditional medicine and modern pharmacology, where they have been used to boost the ability of athletes and more. However, despite decades of research, many aspects of Cordyceps biology remain unexplored, particularly the molecular mechanisms behind their host manipulation and their broader ecological impact. Future studies may not only deepen our understanding of these fungi but also unlock new biotechnological and medical applications. Cordyceps serve as a testament to nature’s ingenuity, bridging the microscopic world of fungi with the macroscopic consequences of parasitism, survival, and adaptation. And lastly, let’s hope that we do not become zombies any time soon!
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