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Wasps turn spiders into nest-building zombies

Scientists watched spiders build webs in the lab, some with wasp parasites, some without.

By Brooks Hays
Wasps turn spiders into nest-building zombies
A wasp larva manipulates its spider host. Photo by Takasuka/Kobe University

KOBE, Japan, Aug. 6 (UPI) -- Wasps can be rather cruel. As a study out of Japan reveals, one species of parasitic wasp manipulates spiders into building its nest.

The wasp (Reclinervellus nielseni) begins the mind control games by laying an egg on the abdomen of an orb-weaving spider (Cyclosa argenteoalba). The wasp larva soon hatches and begins feeding on the fluids of the spider's backside.

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At some point, things get stranger.

The wasp larva eats its way farther into the spider's insides and hijacks the nervous system. Like a wicked puppeteer, the larva forces the spider to do its bidding -- chiefly to build a snuggly and protective cocoon-like web.

To confirm that wasp's manipulative abilities, Keizo Takasuka, a behavioral ecologist at Kobe University, decided to conduct some experiments. Takasuka and his colleagues wanted to ensure the spider's web building wasn't simply a coincidence -- that it was, indeed, coercion.

So the scientists watched spiders build webs in the lab, some with wasp parasites, some without. Orb spiders build two types of nests, a sparser and more traditional hunting nest, as well as a cozier resting nest for when the spider is molting.

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All of the parasite spiders built resting nests. But that fact alone wasn't enough to exclude the possibility of coincidence.

When researchers examined the parasitic and nonparasitic resting nests, they appeared the same. But upon closer examination, researchers noticed the parasite spiders added a few extra protective features.

When UV rays were shined on the webs, the webs of wasp-controlled spiders glowed more brightly. Scientists believe a more reflective web may help protect the pupating wasp and keep other insects from colliding with the nest.

Scientists also found the parasitic nests were reinforced with extra silk and those require more force to break apart -- up to four times stronger than the non-parasitic resting webs.

When all this extra work is done, the wasp hatches and eats the spider.

Researchers aren't exactly sure how the larva renders such control over the spider, but Takasuka suggests the parasite likely injects a hormone into the spider that directs its molting behavior to go into overdrive.

The new research was published in the journal Experimental Biology.

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