[6] It was widely believed that molestus originated in London Tube <100 years ago, representing one of the most rapid events of adaptation and speciation.

[7][8][9][10] However, recent meta-analysis and large-scale genomic study[11][12][13] have found that molestus instead evolved aboveground in the Middle East ~2000 years ago, likely adapting to ancient human agricultural societies.

molestus then colonized belowground habitats like subways and basements in northern Europe (and subsequently across the globe) as humans have developed modern cities more recently.

Also, the Fonseca paper argued that the colonization of America by Culex mosquitoes involved a strain derived from a hybrid of "genetically distinct entities:" C. pipiens and another which, "for the sake of brevity," they called "C. molestus".

They suggested that hybridization might explain why the American form bites both birds and humans (this interpretation is controversial, see letter from Spielman et al.[20] and the response that follows it in Science).

The consequences of its indiscriminate feeding hit the news in 1999 with the outbreak of human encephalitis in New York, caused by West Nile virus.

It was the first documented introduction of this virus into the Western Hemisphere; perhaps because in the longer established populations, the Old World northern above-ground C. pipiens almost exclusively bites birds, with the human-biting ones being incarcerated below ground.

The city government did not make this infestation of the pest a top priority because they tested negative for West Nile virus and because of the high cost of mosquito control.

[22] In Australia, Culex pipiens f. molestus was first recorded in the 1940s, and has since spread across all southern states, causing a significant biting nuisance in urban areas.

Its introduction was likely through military movements into Melbourne during World War II, and genetic studies have indicated its most likely passage was from eastern Asia and Japan.