We’re all familiar with the fearsome tale of the “zombie ants.” As the Inquisitr previously reported, these poor creatures, generally belonging to various species of carpenter ants, are infected by a deadly fungus called Ophiocordyceps unilateralis sensu lato, which takes over the insect’s body and commands it to kill the rest of the colony in a very strange manner.
Ophiocordyceps needs the ant’s body in order to multiply and release its fatal spores. But having an infected ant stay on the ground wouldn’t do much in terms of fungal transmission since “Zombie ants” don’t actually viciously attack the colony to spread the disease.
Instead, the fungus came up with a clever trick: it highjacks the ant’s body and commands it to climb high up a nearby tree. There, the ant chomps into a leaf and remains attached until its body is consumed by the growing fungus, and the parasite blooms into a stalk rising from the back of the ant’s head.
This cruel but highly intelligent mechanism allows Ophiocordyceps, also known as the “Zombie ant fungus,” to use the ant as a puppet and shower the colony below with spores, raining death upon its fellow ants.
As if this wasn’t terrifying enough, entomologists from Pennsylvania State University discovered that the killer Ophiocordyceps fungus is actually more intelligent than previously thought and that it has adapted to climate change in order to ensure its survival, Phys.org reports.
During an expedition into the forests of Sanda in southern Japan, Penn State’s Raquel Loreto stumbled upon a familiar yet bizarrely strange sight. The “Zombie ants” she encountered in this deciduous forest were very different from the specimens she had seen on numerous occasions in the tropical, evergreen forests of South America.
For one thing, they had settled a lot higher up the trees. And, for a mysterious reason, instead of biting into leaves, the “Zombie ants” were wrapped around twigs and hanging upside down.
In a study published yesterday in the journal Evolution, the entomologist argues that this peculiar phenomenon is actually an evolutionary adaptation that helped the “Zombie ant fungus” survive in temperate climates, where trees lose their foliage in the winter.
By commanding the “Zombie ant” to latch onto something more durable, in this case twigs, the fungus manages to stay in place until the next year, when it’s ready to release its spores.
This is a major difference from the Ophiocordyceps species found in tropical areas, where the fungus reaches full maturity in one or two months and doesn’t need to worry about falling leaves.
The finding suggests that the killer fungus has learned to adapt to its environment, particularly to the cooler temperatures and seasonal shift of temperate areas. By doing so, the fungus modified its life cycle to have enough time to produce spores and switched to commanding its “Zombie ant” host to bite twigs instead of leaves.
“Some of the ants do not simply bite the twigs but wrap their back legs around the twig and hold on,” said Loreto.
“They probably do this because biting twigs in not enough to hold them on,” she points out.
In fact, the entomologist has discovered that the “Zombie ant fungus” actually keeps the ant secured to the twig with the help of its hyphae, or the filaments that make up its mycelium.
“The hyphae of the fungus growing out of the [ant’s] legs work as glue on the twig as well,” Loreto explained in a statement.
This unbelievable discovery was proven to be an evolutionary adaptation once Penn State researchers examined DNA samples from the “Zombie ants.” The results uncovered that, from a genetic standpoint, the new behavior of twig biting and leg wrapping developed independently to help the fungus adapt to temperate vegetation.
“We can estimate that these changes occurred between 40 and 20 million years ago,” said study co-author David Hughes.
“However, because of the scarcity of zombie ant fossils, we can’t be any more specific than that at the moment,” he noted.
The timeline came from a 47-million-year-old leaf fossil discovered in Germany which has clear ant bite marks. This fossil formed at a time when temperatures it the area were a lot hotter, before the territory went through the cooling period that settled it into a temperate climate.
This suggests that the leaf biting behavior precedes the twig biting strategy, which evolved as a subsequent adaptation to climate change, says Hughes.
“What is remarkable here is that we have shown that the complex manipulation of an animal by microbe has responded to selection pressure the climate imposes on animals and plants. That was a cool finding that really excited us.”
According to Wired, the same adaptation observed in Japan also occurred in North America, where it evolved independently. Here, the phenomenon is being studied with the help of citizen scientist Kim Fleming from South Carolina, who has been made study co-author and has supplied the team with “Zombie ant” samples from her own backyard.
“As both an excellent photographer and natural historian, Kim was able to collect detailed data for us on the zombie ants over 18 months by taking continual images of samples on her land,” said Hughes.
“This was precious data that would have been very hard to collect,” he revealed.
As a token of appreciation for Fleming’s hard work, the team has named one “Zombie ant fungus” species Ophiocordyceps kimflemingiae, in her honor.