London Underground Mosquito Is Unique

Londoners sheltering from the Blitz in Tube stations during World War II reported being tormented by a particularly aggressive, biting mosquito. This was the world's first major introduction to a unique population that had become trapped and isolated during the construction of the tunnels decades prior. Separated from their surface-dwelling relatives, these insects began a rapid and fascinating evolutionary journey in their new, man-made ecosystem.

Unlike the common mosquito *Culex pipiens* found in London's gardens, which feeds on birds and must hibernate through the cold winter, the subterranean version had to adapt or perish. In the warm, static climate of the Underground, the need for hibernation vanished. With no avian prey available, the mosquitoes shifted their diet to the most abundant mammals: rats and humans. They also adapted to breed year-round in the small pools of standing water found throughout the tunnel network (Review), a different environment from the open ponds and marshes their ancestors required.

These environmental pressures led to significant genetic divergence. Over generations, the underground mosquitoes changed so much that they can no longer successfully interbreed with their above-ground counterparts, a key indicator of speciation. This makes the *Culex molestus*, or London Underground mosquito, a compelling, real-time example of evolution, with a distinct life form being forged in the depths of a modern city.