"The Acrotaphus wasps we studied are very interesting as they are able to manipulate the [behavior] of the host spider in a complex way," said Ilari Saaksjarvi, a professor of biodiversity research at the University of Turku in Finland and one of the study's researchers. "Host manipulation is a rare phenomenon in the nature, which makes these parasitoid wasps very exciting in terms of their evolution."
The researchers detailed their findings in the journal Zootaxa.
Parasitoid wasps manipulate spiders' behavior
Parasitoids are insects whose larvae feed and develop within or on the bodies of arthropods, such as insects, spiders and crustaceans. Each larva develops on a single insect and eventually kills it.
The parasitoid Acrotaphus wasps parasitize on spiders. A female Acrotaphus attacks a spider in its web and temporarily paralyzes it with a venomous sting. The wasp then lays a single egg on the spider and the egg hatches into a larva. Eventually, the larva eats the spider and pupates to become an adult.
Interestingly, during the time period before the larva gobbles up its host, the spider does not spin a normal web for catching prey. Instead, the parasitoid wasp manipulates it into spinning a special web that protects the developing pupa from predators, Saaksjarvi explained. (Related: Newfound cuckoo wasp species mimics other insects' "language" to raise and feed its young.)
Previously, there were only 11 known species of Acrotaphus wasps. This genus of wasps is very diverse, with many more species awaiting to be found. Saaksjarvi and his colleagues found 15 more species of Acrotaphus wasps in the Amazon Rainforest and the cloud forests of the Andes Mountains.
On top of their parasitic behavior, Acrotaphus wasps are also very interesting to study due to their size and color. "Acrotaphus wasps are fascinating because they are very sizeable parasitoids. The largest species can grow multiple [centimeters] in length and are also very [colorful]," said Diego Padua, a researcher from the National Institute of Amazonian Research in Brazil and lead author of the study.
Padua and his team continue to study parasitoid wasps in the Amazon and in Andes forests. In each trip to these locations, they discover many species of animals that have been previously unidentified.
More animals capable of mind control
There are plenty of parasitic animals with the ability to control their host's mind. For instance, the kamikaze horsehair worm (Paragordius tricuspidatus) hijacks the central nervous system of its host, typically a cricket or a grasshopper, in order to mature.
The worm's final stage of development takes place in water. But since its host does not usually swim, the worm coerces its host into jumping into the nearest body of water. The hapless bug then drowns to death while the worm thrives and reproduces.
The parasite Toxoplasma gondii can also make its host do its bidding. It typically infects mice but can also parasitize humans. Studies show that infected rodents lose their fear of the smell of cats and instead become attracted to a pheromone in feline urine. As such, they become more likely to get caught by cats.
It's less clear whether infection with the parasite, which is called toxoplasmosis, can also affect human behavior. Researchers found evidence of personality changes in infected patients, but this is only a correlation and is therefore far from conclusive. Some researchers also found that toxoplasmosis is unusually common in people with schizophrenia, but it's unclear whether that has anything to do with the mental disorder.
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