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Mention wasps and you are bound to hear exasperated tales of picnic sabotages and painful stings. But as it turns out, humans have it relatively easy, at least compared to some poor spiders that the wasps turn into web-weaving zombie slaves.
The parasitic Reclinervellus nielseni wasps specifically target two species of the orb-weaving Cyclosa argenteoalba spider. The attack begins with a female wasp stinging and temporarily paralyzing one of the spiders. She then glues its eggs onto the incapacitated arachnid's abdomen and flies away. Now it's up to the wasp larva to complete the job.
After the eggs hatch, the parasites latch themselves onto the spider's outer body, feeding off the insect's blood. As time passes, the wasp larva also gains control over the spider's nervous system, transforming the insect into a zombie slave that will obey its orders. In this case, that entails the spider abandoning its daily routine and spending hours weaving a protective web - One that the wasp larvae can use when it is time to pupate.
Though scientists have known about the wasp's controlling techniques for over 15 years, they still had a few burning questions. How did the wasps do it and more importantly what was special about the webs the zombie spiders constructed for their masters?
To find out, a team of scientists from Japan's Kobe University collected a few spider specimens with the parasitic larvae attached to them. Their aim was to observe the webs built by the zombie spiders and compare them with those constructed by insects that were not controlled by wasps.
Orb-weaving spiders commonly build two kinds of webs. The "typical" web which is made from sticky thread and used to catch prey and a "resting" web constructed using silk that is not sticky. The latter web is also adorned with a few ultra-violet light reflecting strands to ensure birds and insects do not crash into it accidentally. This is important because the purpose of the resting web is to provide a secure place for young spiders to shed their hard exoskeletons as they grow.
While the wasps have no use for the "normal" webs, they do need a "resting" web for pupation. However, while a spider requires just two days to molt, the wasp takes ten days to transform into an adult. This means that they need stronger "resting" webs - Ones that can withstand wind, rain, as well as, falling debris.
And since they are not capable of building one themselves, the crafty insects have figured out how to enslave the poor spiders and force them to do the job. According to Keizo Takasuka, the lead author of the study which was published in the Journal of Experimental Biology on May 18, the resting webs constructed by the zombie spiders are about 2.7 times stronger than the ones built by spiders not infected by the parasitic wasps.
What's worse is that as soon as the resting web is complete, the larva molts, kills the spider, and gobbles it up. It then spins the silk-like web into a cocoon and hunkers down for the next ten days to complete its metamorphosis to a pesky wasp. The one thing that remains a mystery is what the wasps inject in the spider to trigger the cocoon building. The scientists speculate that it might be some chemical that mimics spider-molting hormones.
These poor arachnids are not the only beings that are mind hacked by parasitic organisms. Many species of fungi, viruses, tapeworms, bees, etc., have been known to do the same for various purposes, including using the bodies of the "slaves" as nurturing grounds for their young!
Resources: businessadvisor.com, livingscience.com, the verge.com