TWS2022: Pesticides may inhibit blue crab survival

By Joshua Rapp Learn

A common pesticide may affect Atlantic blue crabs. Credit: Rob Bixby

A common pesticide could change physiology and behavior of blue crabs when waterways carry it down to coastal estuaries, which can have larger effects on the ecosystem.

Fipronil is used to treat houses for termites, or to kill ticks on people’s dogs or cats—it’s found in common products pet owners use like Frontline or Termidor. The chemical was also used a lot to kill rice water weevils (Lissorhoptrus oryzophilus), a pest that can cause huge damage to the crops. In all cases, the pesticide can eventually wash into rivers, sometimes through the drains of bathtubs, where people treat their dogs for ticks. Eventually, the fipronil will travel downstream to estuaries where Atlantic blue crabs (Callinectes sapidus) and other creatures live.

Annabeth Rawls conducted this work during her undergraduate degree at Louisiana Tech University. Credit: Courtesy Annabeth Rawls

Blue crabs serve a critical environmental role in estuaries as they prey on snails that would otherwise eat away at marsh plants.

“Nobody thinks of them about being a keystone species, but they are,” said TWS member Annabeth Rawls.

They also play an important economic role. In Louisiana alone, Rawls said they contribute between $100 million and $300 million to the economy and between 2,000 and 3,000 jobs. “It can really impact us more than we think it can,” Rawls said.

In research presented at The Wildlife Society’s 2022 Annual Conference in Spokane, Rawls, who was finishing her undergraduate degree at Louisiana Tech University at the time, and her colleagues tested the effects that fipronil might have on blue crabs. In a lab, they exposed blue crabs to different levels of fipronil, then ran a number of tests to determine what effects the chemical had on the crustaceans.

The researchers observed a number of “disturbing things,” Rawls said, especially in the crabs that were exposed to higher concentrations.

It’s unclear how high the fipronil concentration is in parts of the Mississippi Delta in Louisiana, but high levels could affect crabs’ ability to feed and survive in the estuary and disrupt the food web, Rawls said. Low levels in the experiment had little effect.

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society. Contact him at with any questions or comments about his article.

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