Michael Davis
The Ophiocordyceps unilateralis, also known as the zombie ant fungus, is a parasitic fungus that infects ants and takes over their motor functions. The fungus compels infected ants to climb plants or trees and bite onto a leaf or branch, where the ants eventually die and a mushroom-like fruiting body emerges from their heads, spreading spores to infect other ants. While this fungus is lethal to ants, it does not always infect fire ants effectively, as they have physical and chemical mechanisms to combat infection.
| Characteristics | Values |
|---|---|
| Fungi that kill ants | Ophiocordyceps unilateralis, Entomophthora muscae, Massospora cicadina, Beauveria bassiana, Metarhizium anisopliae, Paecilomyces fumosoroseus |
| Fungi's effect on ants | Reduction in foraging activity, ants become more susceptible to stress, kills larvae, workers, and exposed queens |
| Fungi's effect on ant behaviour | Ants climb a branch and cling to the underside of a leaf before mummification |
| Fungi's effect on ant physiology | Takes over the ant's motor functions, feeds on the ant's innards, drains the ant's body of nutrients |
| Fungi's method of infection | Microscopic spores that attach and penetrate the exoskeleton, fungal cells infiltrate the ant's entire body |
| Ant's defence mechanism | Using venom as a disinfectant, alkaloids in the venom can inhibit the growth of certain species of fungi |
| Fungi's limitations | Do not persist in the environment, may be ineffective against fire ants, may attack non-target organisms |
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What You'll Learn
- The Ophiocordyceps fungus takes over ants' bodies to reproduce
- Ants can be infected by eating fungus-covered food
- Fungi can reduce ant foraging activity and make them more susceptible to stress
- Fire ants have mechanisms to combat fungal infections
- Some fungi don't persist in the environment after release
The Ophiocordyceps fungus takes over ants' bodies to reproduce
The Ophiocordyceps fungus, commonly known as the zombie-ant fungus, infects and takes over ants' bodies to reproduce. This fungus, discovered by British naturalist Alfred Russel Wallace in 1859, is predominantly found in tropical rainforests. The Ophiocordyceps fungus has a unique life cycle that is often compared to something out of a sci-fi movie.
The process begins when the fungus infects a foraging ant through spores that attach to and penetrate the ant's exoskeleton. These spores thrive in warm and humid environments, making the ants' bodies an ideal environment for their growth and reproduction. The yeast stages of the fungus spread throughout the ant's body, producing compounds that manipulate the ant's behavioural patterns.
As the infection advances, the fungus takes control of the ant's muscles and compels it to leave its nest and climb a nearby plant. The ant is directed to a specific height, usually about 10 inches or 25 centimetres above the ground, where the temperature and humidity are optimal for fungal growth. The ant then clamps its jaws onto a leaf vein and waits for death.
After the ant dies, the fungus sends a fruiting body out through the base of the ant's head. This reproductive structure ruptures to release spores, turning the ant's corpse into a launchpad for infecting new ants. The Ophiocordyceps fungus's ability to manipulate its host's behaviour ensures the successful dispersal of its spores and the continuation of its life cycle.
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Ants can be infected by eating fungus-covered food
The Ophiocordyceps fungus, also known as the "zombie ant fungus", infects ants by secreting enzymes that dissolve their exoskeleton. The fungal cells then spread throughout the ant's body, including its head and muscles, but surprisingly, they do not invade the brain. Instead, they send chemical signals to the ant's brain, causing it to behave strangely. Infected ants are compelled to leave their nests and climb plants to a specific height, where the fungus can grow optimally.
Once the ant reaches the ideal height, the fungus makes the ant lock its mandibles around a leaf vein. Eventually, the fungus sends a long stalk through the ant's head, growing into a bulbous capsule full of spores. The spores then rain down onto other ants below, infecting them and perpetuating the cycle.
While the Ophiocordyceps fungus is lethal, it only infects a few ants in a colony at any given time to maintain ecosystem balance. Fire ants, in particular, have physical and chemical mechanisms to combat fungal infections, including using their venom as a disinfectant to inhibit fungal growth. Some fungi are also unable to infect fire ants effectively or persist in the environment after release, limiting their effectiveness as a biological control method.
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Fungi can reduce ant foraging activity and make them more susceptible to stress
Ants are exposed to a wide range of pathogens while foraging outside their nests. Opportunistic scavenging ants can assess the sanitary state of food and detect prey that has died from infection by the entomopathogenic fungus Metarhizium brunneum. Ants have also evolved efficient and non-specific behavioural strategies that limit nest contamination, such as forgoing the retrieval of sporulating dead insects or quickly discarding waste.
However, some studies have shown that a fungus-infected environment can influence the behaviour of foragers, both at the individual and collective levels. For example, the presence of parasitoid flies near an ant nest can lead to a decrease in foraging activity. Similarly, microparasites such as fungi, viruses, or bacteria could shape the strategies of food exploitation in ants. These microparasites are assumed to exert a strong selective pressure on insect societies, as they are composed of genetically related individuals living at high densities in confined nests.
Fungi can indeed reduce ant foraging activity and make them more susceptible to stress. Some ant-attacking fungi can cause a reduction in foraging activity, make fire ants more susceptible to stress, and kill larvae, workers, and exposed queens. For example, the Ophiocordyceps unilateralis fungus infects a foraging ant through spores that attach and penetrate the exoskeleton and slowly takes over its behaviour. As the infection advances, the enthralled ant is compelled to leave its nest for a more humid microclimate that’s favourable to the fungus’s growth.
However, it is important to note that not all fungi are effective in infecting ants or persisting in the environment. Some fungi do not culture well in the lab or do not infect fire ants effectively. Additionally, fire ants have physical and chemical mechanisms to combat infection, growth, and/or the effects of various fungi. For example, they can use their venom as a disinfectant, as the alkaloids in their venom can inhibit the growth of some fungal species.
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Fire ants have mechanisms to combat fungal infections
Fire ants are resilient insects that have developed several mechanisms to combat fungal infections. Fungi can be highly dangerous to ants, with some species even taking control of their hosts' behaviour. Despite this, fire ants have a range of physical and chemical defences that can prevent, control, and treat fungal infections.
Firstly, fire ants can use their venom as a disinfectant. Alkaloids in the venom can inhibit the growth of some species of fungi, including Beauveria bassiana, Metarhizium anisopliae, and Paecilomyces fumosoroseus. Fire ants can also use their venom to disinfect their food sources. For example, Myrmica rubra ants can avoid retrieving prey covered in fungal spores, and several ant species avoid food contaminated with Metarhizium brunneum entomopathogenic conidia.
Secondly, fire ants have social defences that they perform at the colony level. They can change their sanitary behaviours depending on the type of fungus attacking them. For instance, weakly infected ants can reduce their risk of superinfection by decreasing allogrooming (grooming another ant) and increasing the application of antifungals towards contaminated nestmates. Furthermore, exposure to a non-mortal fungal infection can promote immunization against future exposures and among non-infected nestmates through the social transfer of the fungal pathogen.
Fire ants also have some individual-level defences. For example, the food filters in the "throats" of some fire ants may be small enough to filter out fungal spores. Additionally, some M. rubra colonies choose to dig their nests in conidia-free substrates to avoid exposure to fungal spores.
Fire ants are highly adaptable insects that can deploy a variety of strategies to combat fungal infections. While some fungal species can control the behaviour of ants, fire ants have a range of physical, chemical, and social mechanisms to defend themselves.
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Some fungi don't persist in the environment after release
Fungi are essential for the decomposition of organic matter and play a fundamental role in nutrient cycling and exchange in the environment. They have been used as a food source by humans for a long time, in the form of mushrooms and truffles. Fungi are also used to make bread and ferment various food products, such as wine, beer, and soy sauce. Additionally, they have been employed in the production of antibiotics and enzymes used in detergents and industrial processes. Fungi are even used as biological pesticides to control weeds, plant diseases, and insect pests.
Despite their benefits, some fungi do not persist in the environment after release. This characteristic has implications for their use as biological control agents against fire ants. When applied to a fire ant mound, certain fungi effectively kill the ants within that specific mound. However, these treatments are more expensive and time-consuming since each mound needs to be treated individually with a significant amount of the product.
Furthermore, there is a concern that these fungi might spread into non-target environments and attack beneficial and desirable insect populations. Not all fungi are species-specific, and they may infect organisms beyond their intended targets, potentially disrupting ecosystems. Fire ants, for example, have physical and chemical mechanisms to combat fungal infections. They can use their venom as a disinfectant, and the alkaloids in their venom can inhibit the growth of certain fungal species.
Additionally, the food filters in the "throats" of some fire ants may be small enough to filter out fungal spores, preventing infection. These limitations highlight the challenges of using fungi that do not persist in the environment as a sustainable solution for fire ant management.
While some fungi do not persist in the environment, others, such as Ophiocordyceps, have been observed to turn their ant hosts into "zombies." This parasitic fungus infects ants through spores that attach and penetrate their exoskeletons. As the infection progresses, the ant is compelled to leave its nest for a more humid environment that favors the fungus's growth. Eventually, the ant sinks its jaws into a leaf vein and waits for death, becoming a launchpad for the fungus to jettison its spores and infect new hosts.
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Frequently asked questions
Yes, some mushrooms can kill ants. For example, the Ophiocordyceps species of fungi infects carpenter ants, taking over their minds and causing them to climb plants and cling to leaves before they die. Once the ant is dead, the fungus sends a mushroom-like fruiting body out through the base of the ant's head, spreading its spores to infect other ants.
Mushrooms can kill ants by infecting them with spores that attach and penetrate their exoskeletons. The Ophiocordyceps fungus, for instance, feeds on the ant's innards and takes over its motor functions, causing it to climb higher where the spores can spread further.
After an ant dies, the mushroom sends a fruiting body out through the ant's head, turning its corpse into a launchpad from which it can spread its spores and infect new ants.
Yes, mushrooms can be used as a natural alternative to conventional pest control for ants. Paul Stamets, a mycologist, used a pre-sporulating strain of the Ophiocordyceps fungus to get rid of carpenter ants in his house. He grew the fungus on rice, which the ants consumed, and a few days later, he was ant-free.
Yes, there are potential downsides to using mushrooms for ant control. Firstly, some fungi do not persist in the environment after release, meaning they only kill ants in the specific mound treated. This can increase the time, labour, and product costs associated with ant control. Additionally, there is a risk that the biological control agent may spread into non-target environments and organisms, adversely affecting ecosystems. Furthermore, some ants have physical and chemical mechanisms to combat fungal infections, reducing the effectiveness of this method.
