This sounds like the plot of the world's smallest horror film: deep in the Ecuadorian Amazon, a newly discovered wasp species turns a "social" spider into a zombie-like drone who abandons his colony to answer as he pleases.
This is the macabre and real discovery of researchers at the University of British Columbia, detailing the first example of a manipulative relationship between a new Zatypota wasp species and a social Anelosimus eximius spider in a study published recently in Ecological Entomology.
"Wasps manipulating the behavior of spiders have already been observed, but not at such a complex level," said Philippe Fernandez-Fournier, lead author of the study and former master's student at the Zoology Department of the University of Montreal. University of British Columbia. "Not only does this wasp target a species of social spider, but it makes her leave her colony, which she rarely does."
Fernandez-Fournier was in Ecuador to study different types of parasites that live in nests of Anelosimus eximius spiders, one of the 25 species of "social" spiders in the world. They are distinguished by their cohabitation in large colonies, their cooperation in capturing prey, the sharing of parental duties and their limited distance from basket-shaped nests.
When Fernandez-Fournier noticed that some spiders were infected by a parasitic larva and saw them moving away from one or two of their colonies to weave silk webs and very tight foliage, he was intrigued. "It was very strange because they did not do it normally, so I started taking notes," he said.
Intrigued, he cautiously brought back to the laboratory some of the structures, called "cocoon cloths," to see what would emerge from the depths.
To his surprise, it was a wasp.
"These wasps are very elegant and graceful," said Samantha Straus, co-author of the study and PhD student. student at the Department of Zoology UBC. "But then they do the most brutal thing."
Using data collected in Ecuador for different projects between 2012 and 2017, researchers began to reconstruct the life cycle of the wasp and its parasitic relationship with the spider.
What they found was both fascinating and horrible: after an adult female wasp has laid an egg on the belly of a spider, the larva hatches and attaches to its unfortunate arachnid. He then presumably feeds on the hemolymph resembling the spider's blood, swells and slowly gains his body. The spider now "zombified" leaves the colony and spins a cocoon for the larva before patiently waiting to be killed and consumed. After being feasted on the spider, the larva enters its protected cocoon and comes out completely formed nine to eleven days later.
In other similar cases of parasitism, wasps are known to target solitary species of spiders such as orb weavers and to manipulate them into behaviors that belong to their normal repertoire.
"But this behavior change is so difficult," said Straus. "The wasp completely diverts the behavior and brain of the spider and makes it do something that it would never do, like leaving its nest and turning on a completely different structure." It's very dangerous for those tiny spiders. "
It's unclear how the wasps do that, but scientists believe that this can be caused by an injection of hormones that gives the spider the impression of being in a life stage different or dispel it from the colony.
"We think wasps are targeting these social spiders as they are a large host colony and a stable food source," Straus said. "We also found that the larger the spider colony, the more likely it was that these wasps would target it."
Straus, who now sports a wasp tattoo, will return to Ecuador to check if the wasps are returning to the same generation-to-generation spider colonies and what evolutionary benefits might present.
Meanwhile, wasps will likely continue their main role in the worst nightmares of spiders.
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Philippe Fernandez-Fournier et al, Behavioral modification of a social spider by a parasitoid wasp, Ecological Entomology (2018). DOI: 10.1111 / een.12698