Scientists discover new parasitic wasp that creates spider zombies

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University of British Columbia Science

In the Ecuadorian Amazon, a newly-discovered wasp is turning a regularly social spider into a lone, lumbering zombie.

The species of spider, Anelosimus eximius, create elaborate bucket-like webs with thousands of its family members. It's deemed a "social spider" because it cooperates with other spiders of its communal home in sharing hunting, parenting and feeding duties.

That is, until a Zatypota parasitoid wasp lays an egg on its abdomen.

Once the wasp's deposited egg hatches, a larva emerges, attaching itself to the spider and feeding on it, sucking on the blood-like haemolymph to survive. At this point, the spider's behaviour changes and it becomes enslaved by the larva, moving away from its communal nest to create a cocoon-shaped web of its own.

The larva feeds on the spider until it dies, in the relative safety of the cocoon-shaped web its host just built before spinning its own cocoon and, eventually, emerging as a beautiful, regal wasp.


Philippe Fernandez-Fournier noticed the strange spider behaviour and started to investigate. Anelosimus eximius don't usually abandon their nests, but when he saw one crawl off to make an entirely new web, he was intrigued.

His research, published in Ecological Entomology, suggests that the larva of Zatypota species of wasp is able to manipulate its hosts activity, controlling its behaviour and forcing it to build these unusual webs -- and it may be the most advanced behavioural manipulation ever seen.

Fernandez-Fournier and his research team suspect that the wasp causes behavioural changes in the spider by "tapping into some ancestral dispersal programme" ... which sounds an awful lot like brain control. Either that or the wasp causes the spiders to starve, which forces them to seek food at the periphery of the nest. Once they get out, they begin spinning webs unlike those they normally inhabit.

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In the animal kingdom, the zombifying capabilities of wasps are not a new thing. Other spider species, such as the Orb Weaver, also become unwilling hosts for wasps and there are species of wasps that do this to cockroaches, too. However, the newly-discovered wasp appears to alter the web-building and social behaviour of this particular species of spider much more intensely than has been seen before.

How can the wasp larva do this? The answer to that question isn't as easy to find but several theories have been posited, including the injection of hormones into the spider that hijack the host's tendency to build "reduced webs during moulting". Other species of parasitoid wasps sting their hosts' brains with a chemical cocktail.

The researchers also discovered that the size of the spider colony plays a role in the amount of spiders that receive the zombie treatment, with larger colonies seeing a higher number of parasitized spiders. That may seem like an obvious connection to make, but it is important to establish the dynamic between parasite and host and may enable further understanding of the evolutionary mechanisms at play in the, admittedly grim, relationship.


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