Deep in the Ecuadorian Amazon, a newly-identified species of the parasitoid wasp genus Zatypota transforms Anelosimus eximius, one of only about 25 species of ‘social’ spiders worldwide, into a zombie-like drone that abandons its colony to do the wasp’s bidding.

“Wasps manipulating the behavior of spiders has been observed before, but not at a level as complex as this,” said University of British Columbia researcher Philippe Fernandez-Fournier.

“Not only is this wasp targeting a social species of spider but it’s making it leave its colony, which it rarely does.”

Fernandez-Fournier was in Ecuador studying different kinds of parasites that live in the nests of a species of social spider called Anelosimus eximius. These spiders are notable for living together in large colonies, cooperating on prey capture, sharing parental duties and rarely straying from their basket-shaped nests.

When the scientist noticed that some of the spiders were infected with a parasitic larva and spotted them wandering a foot or two away from their colonies to spin enclosed webs of densely spun silk and bits of foliage, he was puzzled.

Intrigued, he carefully took a few of the structures, known as ‘cocoon webs’ back to his lab to see what would emerge from the depths. To his surprise, it was a parasitoid wasp species of the Zatypota genus.

“These wasps are very elegant looking and graceful. But then they do the most brutal thing,” said Samantha Straus, PhD student at the University of British Columbia.

Using data gathered in Ecuador, the researchers began to piece together the life cycle of the wasp and its parasitic relationship to the spider.

“What we found was equal parts fascinating and horrifying: after an adult female wasp lays an egg on the abdomen of a spider, the larva hatches and attaches itself to its hapless arachnid host,” they said.

“It then presumably feeds on the spider’s blood-like hemolymph, growing larger and slowly taking over its body.”

“The now ‘zombified’ spider exits the colony and spins a cocoon for 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 instances of parasitism, wasps are known to target solitary species of spiders like orb weavers and manipulate them into behaviors that are within their normal repertoire.”

“The wasp completely hijacks the spider’s behavior and brain and makes it do something it would never do, like leave its nest and spinning a completely different structure. That’s very dangerous for these tiny spiders,” Straus said.

It’s not known how the wasps do this, the team believes it may be caused by an injection of hormones that make the spider think it’s in a different life-stage or cause it to disperse from the colony.

“We think the wasps are targeting these social spiders because it provides a large, stable host colony and food source,” 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 a paper published in the journal Ecological Entomology.

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Philippe Fernandez-Fournier et al. Behavioural modification of a social spider by a parasitoid wasp. Ecological Entomology, published online November 4, 2018; doi: 10.1111/een.12698