An army of zombie slave spiders controlled by their parasitic wasp masters? It might sound like the plot of a cheesy 1960s sci-fi movie, but believe it or not, it actually happens in nature, as the authors of a Journal of Experimental Biology paper published Thursday explained.
According to study author Keizo Takasuka from Kobe University in Japan, these wasps are able to incapacitate unsuspecting insects and arachnids by seizing control of their nervous systems. Once the wasp has a bug or spider under its spell, so to speak, it deposits an egg on or within the body of its victim, paving the way for the next generation to continue the cycle.
One wasp in particular, Reclinervellus nielseni, seizes control of a spider, Cyclosa argenteoalba, which it then commands to construct a tough cocoon-type web out of its original orb-type web in order to protect the developing wasp pupa following the death of the host arachnid.
How do these wasps make spiders do their bidding?
Takasuka explained that the wasps use “chemical manipulation” to exercise its influence upon its victims. In a previous study, researchers removed the manipulating larva from a spider and found that the manipulated arachnid continued web building for a short time afterwards, suggesting that the larval effect “would be chemical, not physical” in nature.
“Until its pupation, the larva keeps the spider alive to let it capture prey as usual,” the author told redOrbit via email. “To catch prey, a spider has to construct a normal trapping web – an orb web. But such snare webs are too fine and fragile in general to sustain wasp’s pupal stage, because this wasp larva murders the spider before pupation. The larva thus has no way to maintain the web in the pupal stage, and thus has to seize control of the spider to reinforce the web.”
Takasuka studied spiders at shrines in the cities of Tamba and Sasayama from mid-April to mid-May, but the researcher had a difficult time keeping some of the spiders alive before their zombie state was triggered. Some of the arachnids would not build webs while in captivity, and Takasuka himself occasionally accidentally destroyed the webs.
How the experiments were conducted
Eventually, however, he was able to observe spiders build 10 carefully constructed cocoon webs for their wasp masters. A careful analysis of the webs revealed that they were similar to the other types of webs they produced, complete with decorative, fluffy structures. By watching the work, he also found that controlled spiders always built the new cocoon webs on the site of the old orb ones, removing the sticky spiral first, then reinforcing it and adding the decorations.
“During my field work, I found the cocoon web of this system for the first time and noticed… the resemblance between the cocoon and resting webs,” Takasuka said, adding that this caused him to expect that the larva exploited the spider’s innate resting web for its own purposes. Behavioral observations, examinations of web function, and quantitative tests of the web followed.
He told redOrbit via email that both types of webs had “specific fibrous decoration” and were generated in a nearly “identical” way. This led him to hypothesize that the fibrous decorations served some function. He conducted reflectance spectrum analysis and found that “decorations on both webs reflects UV light,” which acted as a way to announced the web’s presence to keep other creatures from bumping into it.
Takasuka added that he recruited material strength scientists from the Kobe University Faculty of Engineering. After testing the tensile strength, they found that the cocoon web was more reinforced than the other types of web produced by the spiders. Finally, he used unparasitized spiders of the same species, and replaced them over time with parasitized ones. Eventually, he was able to see several wasp larvae reach pupal stage and go on to manipulate the spiders.
(Image credit: Keizo Takasuka)
Comments