SW New Mexico News

Researchers at New Mexico State University (NMSU) have been exploring the effectiveness of traditional insect repellent methods used by Native Americans, involving rancid animal fats. The study was initiated by Texas archaeologist Gus Costa, who collaborated with NMSU biology professor Immo Hansen's lab to test historical accounts documented by Spanish conquistadors. These accounts suggested that Native Americans in the Gulf Coast area used rancid fats from animals like sharks and alligators to ward off mosquitoes.

"Gus started procuring fats and making them rancid and sending them to us," said Hansen. "That took about five years as we went back and forth. We also sourced our own oils and did the same experiments. Last year, it all came together, and we wrote a paper on it."

The findings were published in August in PLOS ONE under the title “Rancid rumors or Native wisdom: Evaluating the efficacy of animal fats as insect repellents attributed to historic-period Native Americans.” The research team included Hailey Luker, an NMSU biology Ph.D. candidate, Claudia Galvan, lab manager for co-author Omar Holguin from NMSU's Department of Plant and Environmental Sciences, with Acosta as the senior author.

The study tested various rancid animal fats including those from alligator, cod, shark, bear, beef tallow, and pig lard for their mosquito-repelling properties. Researchers ensured these fats were ethically sourced.

“When a fat or oil becomes rancid, that doesn't necessarily mean it smells bad; it just means that it has an odor,” explained Luker.

Galvan noted an interesting observation: “What we found that is interesting is if they’re not rancid, they had lower levels of repellency; if they are rancid, they’re at higher levels.”

Using yellow fever mosquitoes (Aedes aegypti), the team conducted arm-in-cage assays to assess protection times when these substances were applied to human skin. They also evaluated long-distance repellency using a Y-tube olfactometer assay and tested tick-repellency through crawling assays.

The results indicated that while rancid animal fats from cod, bear, and alligator are effective mosquito repellents over short periods, both fresh and rancid fats do not repel ticks. This supports traditional ethnozoological knowledge held by Native American communities.

“For the rancid fats we don't yet know the active ingredient that repels mosquitoes,” Hansen stated. “We really want to find out about the active ingredients in this big mixture of different chemicals that Claudia has produced.”

Galvan emphasized learning from historical remedies: “There are a lot of traditional remedies that go back centuries... So I think that the full circle message of this study is definitely something that we can really learn from but then we can also improve.”