Don’t tread on me: Snake paper retracted for ‘soft-stepping’ technique

Agitating snakes isn’t something most of us would do on purpose, but for a group of researchers, it was central to their research. The authors of a May 2024 paper in Scientific Reports achieved that by “softly” stepping on the head, tail and mid-body of newborn, juvenile and adult pit vipers to see how often they would bite. 

But the technique wasn’t quite what the authors’ ethics committee had in mind when approving the study. The journal retracted the paper last month, noting the ethics approval the authors received “did not include newborn snakes or the use of the ‘soft stepping’ method.” 

Lead author João Miguel Alves-Nunes blamed the retraction on a “communication error” by the ethics committee. The researchers believed they had approval both to step on snakes and to include newborn snakes, Alves-Nunes, a former researcher at the Butantan Institute in São Paulo, Brazil, said in an email to Retraction Watch. 

Two methods were initially approved by the ethics committee, Alves-Nunes said. One “involved touching and pressing the snake’s body against the ground using a metal herpetological hook.” The second consisted of researchers approaching the snakes with a booted foot. 

The researchers “noticed that the metal hook could injure the snakes’ mouths,” so rather than using the hook to press down on the snake, they lightly stepped on the animals instead, Alves-Nunes said. The boot had a foam reinforcement to protect the snakes, he told us. 

Alves-Nunes said the researchers “did not even consider that this modification required an additional approval request, as this method was essentially a combination of the two already approved methods.” 

As reported in a Q&A with Alves-Nunes in Science, he stepped on 116 snakes 30 times each, totaling over 40,000 steps. In tests with a different type of snake, the bite pierced his boot. That’s when he learned he is allergic to snake venom and antivenom.

Mid-study, the researchers began questioning how hatchlings would react to this method. They submitted a second request to the ethics committee asking permission to include these newborn snakes in the study. 

The committee first rejected this proposal because of Alves-Nunes’ allergy to the snake venom caused by “a history of ophidic accidents,” or snake bites, according to the authors’ rebuttal of the retraction, provided to Retraction Watch.

Once researchers replaced Alves-Nunes with coauthor Adriano Fellone as the “executor” of the experiment, the “Ethics Committee of the Butantan Institute responded with a single word: ‘APPROVED,’” Alves-Nunes said. 

After the retraction, the researchers realized the approval response applied only to Alves-Nunes’ removal from the study, not the use of hatchlings, he told us. 

The Butantan Institute told us the animal ethics committee was unavailable for comment because of a national holiday. 

Readers raised ethical concerns about the study shortly after its publication, Rafal Marszalek, the journal’s chief editor, told us. The paper has been cited six times, according to Clarivate’s Web of Science. 

All authors disagreed with the retraction, the notice states. Alves-Nunes called the decision to retract “disproportionate. The mistake made was bureaucratic, not scientific fraud, plagiarism, or experimental error.”  

The authors’ response to the retraction, signed by senior author Otavio Marques of the Ecology and Evolution Laboratory at the Butantan Institute, noted the researchers “emphasize that ethical conduct regarding live animal experimentation—avoiding excessive suffering and minimizing discomfort and the number of specimens used—was upheld.”

After our story published, we heard from the communications office at the Butantan Institute, who told us by email:

The Institute does not believe that the violation of the methods approved by CEUAIB [the Butantan Institute Animal Use Ethics Committee] was intentional and clarifies that, at this time, there is no ongoing institutional process aimed at penalizing those involved.

This story was updated March 10, 2025, to include a statement from the Butantan Institute.

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