One can find really weird things when walking along a Southeast Asian rainforest path. Common examples are ants, and more rarely other insects or spiders, sitting under a leaf with weird club shaped appendages growing out of them. At closer inspection of the ants in question, it is clear that the ants have their mandibles firmly anchored in the leaf, and, furthermore, that the ants are quite dead. Almost always the arthropods showing such of appendages are positioned right under the leaf, often biting around the leaf stem, thus keeping as dry as possible in the rainy and humid environment of the rain forest.
What has happened to these poor animals? Well, the fungus Cordyceps, or close relatives to Cordyceps, has happened. Cordyceps is a genus of endoparasitic fungi which attack arthropods such as insects or spiders. The attack from the Cordyceps starts when a spore from the fungus gets attached to the outside of the arthropod and germinates. The mycelium of the fungus enters the insect or spider through its breathing apparatus, which consists of small tubes, so called trachea, that transverses the body of the animal (or in the case of spiders, book lungs, that from the perspective of the fungus serves the same function).
The fungus soon starts to grow inside the animal, reaching every corner of the still live animal, converting animal matter to fungus mycelia. After a while, when the fungus more or less have exhausted all non-vital parts of the infected animal, the fungus by chemical means takes control over the ”brain” of the arhtropod. The arthropod is ”told” to climb up in the foliage and attach itself to a leaf, where it sits well protected from the frequent rains. Here the Cordyceps finally kills of its victim, converting the last matter left from insect or spider to fungus. Then the fruiting bodies, the appendages, grow out of the victim, and the fungus starts producing millions and yet millions of spores. Due to the positioning of the now dead victim, these spores are kept quite dry, and can thus spread over quite some distance in the hope of infecting yet another ant.
So is this a aquisition that the ants and other victims of the fungus havent yet had time to evolve a countermeasure to? It turns out that there are 48 000 000 years old remnants of bites of infected ants on fossil leaves. The bite marks are so characteristic that researchers are confident that Cordyceps have been taking over the minds of ants for at least so long. It is somewhat surprising that the ants haven´t been able to adapt to the fungus and evade the quite gruesome effects of getting infected.
Interestingly, some Cordyceps species are considered to have medical effects and have been used in traditional Tibetan medicine as an aphrodisiac. It is quite clear that the Cordyceps fungi group contain biological active chemicals, and some of those are being studied for use in modern medicine. Wouldn´t it be incredibly cool if a 48 000 000 year old chemical used to take over the mind of ants and other arthropods could be used to cure some of our modern day ailments?