Parasitic Worms Transform Spiders into ‘Zombies’ in New Zealand

A study led by PhD student Usha Mendis at Lincoln University has revealed alarming insights into how parasitic worms, known as mermithids, are turning spiders into what some describe as “zombies.” These nematodes infect a variety of invertebrates, including caddisflies, mayflies, and grasshoppers, but their impact on New Zealand’s endemic spider population is particularly concerning.

Mendis has identified three distinct types of spiders that carry these parasites, and her research aims to pinpoint the specific species that are affected. “New Zealand has a large number of endemic spiders; over 90% of them are unique to this region,” she explained. “If something were to happen to them, it would not be good for our biodiversity.” The role of spiders in the food chain is vital, and the presence of mermithids disrupts this balance dramatically.

The process of infection is both slow and deadly for the spider. Mendis notes that infected spiders often exhibit abnormal physical changes, such as enlarged limbs and swollen abdomens. “They look like zombies,” she remarked, highlighting the drastic transformations caused by the nematodes. While the most definitive sign of infection is the emergence of the nematode from the spider’s body after death, there are subtle indicators that may suggest a spider is parasitized.

Researchers are still investigating the mechanisms through which the nematodes infiltrate their hosts. Mendis is particularly focused on understanding what drives these parasitic worms to seek out spiders. “They can’t live without a host. They consume the energy and nutrients of the host and grow inside it,” she stated. To progress to the next stage of their life cycle, the nematodes require moisture, which influences the behavior of infected spiders, often leading them to seek out wet environments where they may ultimately drown.

To collect samples of these nematodes, Mendis is utilizing water traps, a method that highlights the complex interactions between the parasites and their hosts. Despite being first reported in New Zealand only 35 years ago, there is still much to learn about the relationship between mermithids and spiders.

While Mendis’s research delves into the darker aspects of this parasitic relationship, she urges the public to reconsider their perceptions of spiders. “Spiders may look disruptive and creepy, but they’re not the enemy,” she said. “They’ve got their own problems to deal with.” Understanding the ecological role of spiders is crucial as researchers continue to study the implications of mermithid infections on these vital species and the broader ecosystem.