Parasitoid wasps may turn spiders into zombies by hacking their internal code

Parasitoid wasps may turn spiders into zombies by hacking their internal code
A wasp getting ready to attack a spider. Researchers think that it will then use a hormone called ecdysone to change the spider's behavior so that it spins a special kind of web. Credit: Marcelo O. Gonzaga

Parasitoid wasps lay their eggs on a spider's back. This team proposes that by injecting the spider host with the molting hormone, ecdysone, the wasp induces the spider to make a special web for the wasp's pupa.

Setting off a startling chain of events, a parasitoid wasp can force a to weave a special web to suspend the wasp pupa just before it finishes killing its spider host. William Eberhard, staff scientist emeritus at the Smithsonian Tropical Research Institute and Marcelo Gonzaga at the Universidade Federal de Uberlândia in Brazil have assembled wide-ranging evidence that 'zombification' involves hacking existing web-spinning mechanisms by hijacking the spider's own molting hormone, ecdysone.

In a new paper published in the Biological Journal of the Linnean Society they combined a review of all known reports of different wasp species known to zombify different spider species around the world; the results from a molecular study in Brazil; and new observations of Costa Rican spiders to demonstrate several previously unappreciated patterns that suggest that the use ecdysone.

One puzzle the researchers address is how a single wasp species can induce an impressive diversity of changes in the webs of many different spider host species. In the most complex cases, the spider's web construction is affected at several different stages: from selecting a site to modifying several different key design elements that usually result in a sheltered, stable home for its pupal cocoon.

This feat is dramatic because the wasp larva does not have direct contact with the spider's nervous system: it is an external parasite, riding on the surface of the spider's abdomen. Its only access to the spider's brain is via injections of psychotropic substances into the hemolymph in the spider's abdomen, to then be carried by the spider's to its central nervous system.

Parasitoid wasps may turn spiders into zombies by hacking their internal code
Now fully developed, the wasp larva proceeds to eat its host spider. Credit: Marcelo O. Gonzaga

"Several studies suggested that sometimes the webs induced by the resemble the webs that unparasitized spiders build just prior to molting," said Gonzaga. "We combined that observation with a previous discovery that, in one genus, spiders that had just built cocoon webs had unusually high concentrations of ecdysone in their bodies, and predicted that the specificity of the wasp larva's effects may already be present in the spider's , in the form of its specific behavioral responses to the hormone that controls its own molting cycle. By hacking into this system, the wasps ensure the safety of their own offspring at the expense of their host."

"Now that we have a proposed mechanism, we can ask a new set of questions," Eberhard says. "Because the lines in spider webs represent precise records of their behavior, we could study "zombification" in unprecedented detail by looking at the lines in cocoon and molting webs. We discovered that both web types vary, and more importantly, that the variations only overlap partially.

Parasitoid wasps may turn spiders into zombies by hacking their internal code
After eating the spider, this wasp is now in its pupal stage and hangs from the spider's molting web. Credit: Marcelo O. Gonzaga

"The larvae probably tweak the spider's molting web construction behavior to gain added protection. The mechanisms by which these additional modifications are obtained may result from differences in the timing or amounts of ecdysone, or modifications in the ecdysone molecules themselves, but they remain to be documented," Eberhard continued.

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More information: William G Eberhard et al, Evidence that Polysphincta-group wasps (Hymenoptera: Ichneumonidae) use ecdysteroids to manipulate the web-construction behaviour of their spider hosts, Biological Journal of the Linnean Society (2019). DOI: 10.1093/biolinnean/blz044
Citation: Parasitoid wasps may turn spiders into zombies by hacking their internal code (2019, April 29) retrieved 16 October 2019 from
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Apr 29, 2019
Fantastic but horrific method devised by wasps for self-preservation

Apr 29, 2019
Looks horrific to a creature with 10 trillion synapse paths, but it's just life and death in the big jungle for creatures with merely a million or so.

A spider cannot conceive of "death" as we perceive it. It has no self awareness. Its death is no more significant than you turning off your computer, and in fact less so: your computer has thousands of times more synapses than a spider.

And spiders are a very successful life form.

So are wasps.

Apr 30, 2019
Depends what you mean by 'self awareness'. Maybe they are self aware.
A spider cannot conceive of "death" as we do since it's not sentient. It's not sentient because it can't imagine other minds, or itself, thinking. Our brains evolved specifically to enable us to model other minds, we are super social animals after all. This make it possible to think about yourself dying.
A spider knows this is 'me' and out there is the rest of the world. It has a 3D model of the world in it's head. It can recognize other animals, distinguish predators from prey from irrelevant passers by from inanimate objects. It can be creative in solving puzzles. It can plan ahead, it can learn and remember. Spiders can be unbelievably smart. Some are social and can recognize individuals.
Portia's hunting techniques and social behavior:
Can a spider fear death?
I dunno, but they certainly seem terrified of things that could eat them.

Apr 30, 2019

I dunno, but they certainly seem terrified of things that could eat them.

And we have 200+, so far, putative pathways for pain to be registered by our own central nervous system. No doubt arachnids share some of them, and have some of their own - pain is a shared signal and motivation system.

Nature, red in tooth and claw; evolution is a killer, as it has to be. (Okay, so population generations compete and while many lineages are chemotrophs or plants, why does nature have to like parasites with half of species being such? And while our fellow archaea seem not to thrive on parasitism, we eukaryotes do for some reason or other - ecology is the darnedest thing.)

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