Brazilian ecologist who migrated to the US in 1976 discovered why mosquitoes love human blood

Mosquito attraction to human study: Walter Leal has spent decades studying insects, but one question stood out: why are mosquitoes so attracted to humans? His research identified a natural compound called nonanal, produced by humans and birds, that Culex mosquitoes find irresistible.

Leal, a Brazilian chemical ecologist and professor of entomology at the University of California, Davis, even tested the idea on himself before asking others to participate, as per a report.

Walter Leal tested his own skin for mosquito-attracting odor

To find out whether humans produce a natural chemical that attracts mosquitoes, Leal volunteered as the first test subject, as per a Livescience report.


Researchers placed a syringe-like device next to his skin and wrapped his arm in aluminum foil to create a sealed environment. After an hour, they analyzed the collected sample to measure levels of nonanal, a compound produced by humans and birds.

Leal said, "It's there. I have lots of it," adding, "I think I released 20 nanograms in an hour. It was high," as quoted by Livescience.

The discovery helped explain why mosquitoes targeted him

Leal said the findings reminded him of a beetle-hunting trip to Mexico two years earlier, where mosquitoes relentlessly bit him despite using insect repellent.

He recalled spraying DEET everywhere, including in his hair, yet waking up covered in bites after mosquitoes found exposed areas, even biting through his thick socks.

According to Leal, mosquitoes can detect body heat and will find even small uncovered spots.

Years of research into insect communication

Leal is widely known for studying insect pheromones and chemical communication, research that has applications for pest control.

He also discovered why mosquitoes avoid DEET, explaining that they are repelled by its smell. Over the years, he has identified and synthesized pheromones from insects including scarab beetles, true bugs, longhorn beetles, moths, navel orangeworms and cockroaches, as per the Livescience report.

From Brazil to the United States

Leal grew up in Recife, Brazil, and first traveled to the United States in 1976 as a student to help broadcast news about Brazil's soccer team during the Bicentennial World Cup.

He later earned a bachelor's degree in chemical engineering from the Federal University of Pernambuco before completing a master's degree in agricultural chemistry at Mie University and a doctorate in applied biochemistry at Tsukuba University in Japan, where he spent 16 years working, most of them for the Japanese government, according to Livescience report. In 2000, he joined the faculty at the University of California, Davis.