A New Study Rewrites the Origin Story of the “London Underground Mosquito”

For decades, scientists told the incredible story of a mosquito that rapidly evolved within two centuries to bite humans in the underground tunnels of the London subway. While this story never made much sense, the mosquito’s true origins have remained unclear. A new study— published today in Scienceand led by Princeton University’s McBride group, with former graduate student Yuki Haba as lead author—finally uncovers the evolutionary history of the mosquito Culex pipiens form molestus. Haba was a recipient of the HMEI Walbridge Fund Graduate Award for Environmental Research in 2021.

The so-called “London Underground mosquito” — often cited as a textbook example of rapid urban evolution — actually originated over a thousand years ago in the Mediterranean basin, likely among early agricultural societies such as Ancient Egypt.

“We suspected the mosquitoes might have an ancient origin somewhere in the Mediterranean basin,” said Lindy McBride, Associate Professor Ecology and Evolutionary Biology and Neuroscience at Princeton and senior author on the new study. “And when we looked at the data, everything fell into place.”

This finding emerged from a massive interdisciplinary effort spanning 50 countries, involving over 200 co-authors and more than 5,000 email exchanges – a truly global collaboration working together to untangle the mosquito’s mysterious evolutionary history.

“We started reaching out to potential collaborators back in 2018, contacting every Culex pipiens researcher we could find across the globe,” said Haba, who is the lead author of the study and is now a postdoctoral researcher at Columbia University. “We emailed people, talked to people at conferences, and spread the word on social media. The response was overwhelmingly positive – everyone wanted to know more about the confusing history of this human-biting mosquito. By the end of the project we had more than 200 collaborators collecting and sending us mosquitoes all over the world.”

Pictures of some of the Culex pipiens Population Genomics Project collaborators from across the world.

By sequencing 350 mosquito genomes from 77 sites across Europe, North Africa, and western Asia, the team showed that molestus’s adaptation to human environments is not modern, but ancient.

“Our analyses strongly suggest that molestus first evolved to bite and live alongside humans in an early agricultural society 1,000-10,000 years ago, most likely in Ancient Egypt,’” said Haba.

The study also carries public health implications. Culex pipiens is a major vector for West Nile virus — a bird virus that can ‘spill over’ to infect humans when a vector mosquito first bites an infected bird and then bites a human. Previous research links such spillover events to hybridization between molestus and its bird-biting ancestors, which produces mosquitoes willing to bite both types of hosts. However, the two forms are so closely related that hybridization has been difficult to detect.

“Our work provided new insight into how this mosquito varies genetically from place to place — insight that we think will help us better understand the role it plays in transmitting West Nile virus from birds to humans,” said McBride. McBride, Haba, and their collaborators found that hybridization between bird-biting and human-biting forms is far rarer than previously believed, but does occur, especially in cities.

“Our work opens the door to incisive investigation of the potential links between urbanization, hybridization, and spillover of the virus from birds to humans,” said Haba.

The study reshapes our understanding of how human societies influence mosquito behavior and disease transmission. By studying the genome of the molestus form, the researchers provide critical insights for tracking the virus’s spillover and understanding how mosquitoes adapt to urbanization and climate change.