A recently discovered species of wasp in the Ecuadorian Amazon transforms a 'social' spider into a zombie drone who leaves his colony to fulfill the orders of the wasp.
That is the dreadful discovery of real life made by researchers at the University of British Columbia, who detail the first example of a manipulative relationship between a new wasp of the species Zatypota and a social spider Anelosimus eximius in a study recently published in Ecological Entomology.
"The wasps that manipulate the behavior of spiders have been observed before, but not at a level as complex as this", said Philippe Fernández-Fournier, lead author of the study and a former master's student in the zoology department of the UBC. "Not only is this wasp targeting a social species of spider, but it is causing it to abandon its colony, which it rarely does."
Fernández-Fournier was in Ecuador studying different types of parasites that live in the nests of the spiders Anelosimus eximius, one of the approximately 25 species of "social" spiders throughout the world. They are remarkable for living together in large colonies, cooperating in the capture of prey, share the duties of the parents and rarely get away from their nests in the form of a basket.
When Fernandez-Fournier noticed that some of the spiders were infected with a parasitic larva and saw them moving away from their colonies to spin closed nets of densely spun silk and bits of foliage, he was perplexed. "It was very strange because they usually do not do that, so I started taking notes", He said.
Intrigued, he carefully picked up some of the structures, known as "webs of cocoons," back to the lab to see what would emerge from the depths. To his surprise, it was a wasp. "These wasps have an elegant appearance," Samantha Straus, co-author of the study and a student in the zoology department at UBC, said in a statement. "But then they become more brutal". Using data collected in Ecuador for different projects between 2012 and 2017, the researchers began to reconstruct the life cycle of the wasp and its parasitic relationship with the spider.
What they found was equally fascinating and horrifying: after an adult female wasp lays an egg in the abdomen of a spider, the larva hatches and attaches to its hapless arachnid host. Then, presumably, it feeds on the hemolymph, similar to the spider's blood, which gets bigger and takes the body slowly. The now "zombified" spider leaves the colony and spins a cocoon by the larva before patiently waiting to be killed and consumed. After feasting on the spider, the larva enters its protected cocoon, emerging fully formed nine to eleven days later.
In other similar cases of parasitism, it is known that wasps target solitary spider species such as orb weavers and manipulate them into behaviors that are within their normal repertoire. "But this behavior modification is serious"said Straus. "The wasp completely hijacks the behavior and brain of the spider and causes it to do something it would never do, such as leaving its nest and creating a completely different structure, which is very dangerous for these small spiders."
It is not known how wasps do this, but scientists believe that it can be caused by an injection of hormones that make the spider think that it is at a different stage of life or that it is dispersed from the colony. "We believe that wasps target these social spiders because it provides a large colony of stable host and a source of food"said Straus. "We also discovered that the larger the spider colony, the more likely it is that these wasps will target it."
Straus, who now has a wasp tattoo, will return to Ecuador to investigate if the wasps return to the same spider colonies generation after generation and what evolutionary advantage it could present. Meanwhile, the wasps will probably continue their leading role in the worst nightmares of the spiders.