This Pesticide Doesn’t Kill Spiders, But It Does Mess With Their Heads

A common orchard pesticide called Phosmet may give jumping spiders a personality disorder, researchers at McGill university report.

Orchard owners across the U.S. spray the insecticide on orchard trees to thwart the larvae of codling moths. Like any modern pesticide, Phosmet can be pretty toxic at high doses. However, while it's meant to kill moth larvae, it’s not supposed to kill the bronze jumping spiders (Eris militaris) that inhabit the trees and play a key role in orchard health.

And it doesn’t kill them. But, it does make them go a little bit nuts, as the McGill team found.

Animal behavior experiments suggest that jumping spiders can have different personalities, typically shy or bold. When exposed to low doses of Phosmet, jumping spiders start to behave unpredictably, which affected their ability to capture prey and explore new environments. Under the influence of Phosmet, bold spiders aren’t as adept at catching prey, and shy spiders start getting overly aggressive. Dan Nosowitz of Modern Farmer likens the effects to getting the spiders “dangerously” drunk.

The chemical also seemed to affect males and females differently. Females had more trouble pinning down prey, while males seemed to get lost in their own environment. The McGill team’s results appear in Functional Ecology.

Jumping spiders play an essential role in orchards, serving as another level of pest control and keeping leafrolling moths at bay. But, they aren’t the only beneficial critter to face threats from Phosmet. The pesticide has also been linked to problems with native bee foraging and nesting in orchards, explains Nosowitz.

Given that the chemical has these previously unknown impacts on spider behavior, it might be time to take a renewed look at how farmers use Phosmet in orchards.

Helen Thompson | | READ MORE

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.