In the heart of the Ecuadorian Amazon, a newly identified species of the parasitic genus wasp Zatypota transforms Anelosimus eximius, one of the 25 species of "social" spiders in the world, transformed into a zombie-like drone that abandons its colony to meet the expectations of the wasp.
"Wasps manipulating the behavior of spiders have already been observed, but not at such a complex level," said Philippe Fernandez-Fournier, a researcher at the 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 the nests of a species of social spider called Anelosimus eximius. These spiders are known to live together in large colonies, cooperate in catching prey, share parenting tasks, and seldom move away from their basket-shaped nests.
When the scientist noticed that some of the spiders were infected with a parasitic larva and saw them moving away from one or two of their colonies to weave silk webs and bits of foliage, he was surprised.
Intrigued, he carefully took some of the structures, called "cocoon strips," into his lab to see what would emerge from the depths. To his surprise, it was a parasitoid wasp species from the Zatypota kind.
"These wasps are very elegant and graceful. But then they do the most brutal thing, "said Samantha Straus, PhD student at the University of British Columbia.
With the help of data collected in Ecuador, researchers began to understand the life cycle of the wasp and its parasitic relationship with the spider.
"What we found is 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 unhappy host." arachnids, "they said.
"It then presumably feeds on the hemolymph resembling spider blood, swells and slowly gains its body."
"The spider now" zombified "leaves the colony and spins a cocoon for the larva before patiently waiting for it 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 manipulate them into behaviors that are part of their normal repertoire."
"The wasp completely diverts the spider's behavior and brain and makes it do something it would never do, like leaving its nest and turning on a completely different structure. It's very dangerous for these little spiders, "said Straus.
The team thinks that this could be caused by an injection of hormones that would give the spider the feeling of living in a different phase of life or dispelling it from the colony.
"We think wasps are targeting these social spiders because they provide a large stable host colony and a source of food," Straus said.
"We also found that the larger the spider colony, the more likely it was that these wasps would target it."
The discovery is described in an article published in the journal Ecological Entomology.
Philippe Fernandez-Fournier et al. Behavioral modification of a social spider by a parasitoid wasp. Ecological Entomology, published online November 4, 2018; doi: 10.1111 / een.12698