Parasitic Wasps That Take Control of Their Spider Victims Discovered in Amazon Rainforest

Researchers have identified 15 new parasitic wasp species which can manipulate the behaviour of their hosts.

The wasps belong to the genus—or group of species—Acrotaphus which parasitize spiders. Previously, scientists only knew about 11 species in the genus. But a study published in the journal Zootaxa significantly increases that figure, casting new light on the diversity of these animals in the tropics.

The wasps were identified by a team of scientists from the Biodiversity Unit of the University of Turku in Finland—which has been studying the diversity of tropical insects for two decades, uncovering numerous new species in the process—and colleagues from Brazilian institutions.

Females of this genus attack spiders in their webs, and temporarily paralyze them with their sting. The wasp then lays a single egg on the spider and eventually a larva hatches out.

This larva then proceeds to eat the spider before transforming into a pupa—an intermediate stage in the insects's lifecycle during which the larva becomes enclosed in a protective covering.

Intriguingly, Acrotaphus wasps can manipulate the behavior of their host spider. According to the scientists, the insect forces the spider to produce unusual webs before its death which help to protect the developing pupa. This kind of manipulation is rare in nature, the researchers say.

"We more than doubled the species number," one of the authors of the study, Ilari Sääksjärvi from the University of Turku, told Newsweek. "In the case of large-sized and colourful insects, it is quite a good result and, on the other hand, demonstrates that we still have loads of 'unknown worlds' on Earth."

"The species of the genus Acrotaphus are known to manipulate the web-building behaviour of the host species in complicated ways," Sääksjärvi said.

The wasps they found are native to the lowland forests of the Amazon and the cloud forests of the Andes in South America.

"We have been studying the Amazonian and Andean parasitoid wasps for years," Sääksjärvi said. "Most of the new species were found during our expeditions and field sampling programmes. Some of the species were found from the museum natural history collections."

Wasps belonging to the genus Acrotaphus are notable for their size—the largest can grow to lengths of several centimeters—as well as their striking coloration.

"The species of Acrotaphus are large and colorful in comparison with many other spider-attacking parasitoid wasps. This makes them especially interesting and conspicuous in the field," Sääksjärvi said.

parasitic wasp
The tropical parasitoid Acrotaphus wasps manipulate the behavior of their host spiders in a complex way. The species of the genus are large and colorful. Kari Kaunisto