The larva of this wasp species turns the spiders into zombies at their service and then eats them

Scientists have for years controlled the parasites that control the behavior of their hosts for their own benefit, but they have now discovered a disturbing relationship between the larvae of a parasitic wasp and a social spider.

Some organisms appropriate the brains of some carriers, usually for reproductive purposes. The mushrooms O. unilateralisis, for example, they control the brain of carpenter ants. The parasite Diplostomum pseudospathaceum He hides in the eye of the fish and leads him to death.

Now a team of scientists from the University of British Columbia has discovered another interesting parasite relationship. This is one of the most unpleasant we have encountered, both for its complexity and for its baseness. In the new study published today in Ecological Entomology, researcher Philippe Fernández-Fournier describes how the parasitic wasp species Zatypota uses and abuses the social spider Anelosimus eximiususing it first as a vehicle and then forcing it to build an incubation chamber. Ah, finally the spider is eaten.

Fernández-Fournier met this discovery in the Ecuadorian Amazon by studying several parasites living in the nests of A. eximius. These arachnids are known as social spiders because they live in large colonies, work together to capture prey, share reproductive tasks, and rarely venture beyond the confines of their basket-shaped common nests.

As these spiders have a very predictable behavior, Fernandez-Fournier soon realized that some of them were infected with a parasitic larva, to see how far they were from the colony. This observation was already quite rare in itself, but the scientist also observed how these same spiders started spinning dense silk buds and pieces of foliage.

"It was very strange because they usually do not do it, so I started taking notes," Fernandez-Fournier said in a statement.

Moved by curiosity, he took the cocoon to the laboratory. When he opened it, to his surprise, he saw how a wasp was developing in him. Fernández-Fournier and his team have studied in greater depth and discovered an interaction never documented between these two species.

Here's how it works: a female wasp Zatypota puts an egg in the abdomen of a spider Anelosimus eximius. When the larva hatches, it becomes attached to the spider and begins to feed on its blood. The larva grows gradually and begins to absorb much of the spider's body.

Over time, the spider slowly becomes a "zombie" and no longer behaves normally. Under the influence of the larva, the spider leaves its colony and takes charge of forming a network of cocoons. Once this construction task is completed as a slave, the spider remains motionless, allowing the larva to consume until it dies. Satisfied, the larva slides inside the cocoon that the spider has woven and uses as an incubator for its next stage of gestation. After a period of 9 to 11 days, a completely mature wasp emerges from the cocoon. Then the cycle begins again, to the disgrace of his next arachnid victim.

According to the researchers, this strategy is unique in that parasitic wasps have only been documented to attack solitary spiders.

"This behavior change is very serious," said Samantha Straus, co-author of the study, in a statement. "The wasp completely diverts the brain and behavior of the spider and forces it to do something that it would never do, like leaving its nest and creating a completely different structure." is very dangerous for these little spiders. "

Straus added, "We think wasps are targeting these social spiders because they are a large, stable host colony and a source of food, and we have also found that the spider colony is larger. the more likely it is that wasps target it. "

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The researchers believe that the wasp injects a hormone that modifies the spider's brain to hypnotize it. This hormone causes the spider to think that she is at a different stage of her life or is acting as a signal that makes her run away from her colony. For the moment, they do not know exactly how the process that turns the spider into a zombie works. It's just a conjecture.

Fernández-Fournier and Straus now want to return to the Ecuadorian forests to learn more about these evil wasps and their hosts. In particular, they would like to know if the wasps still designate the same spider colonies and, if so, how to exploit them. [Ecological Entomology]