|Culex pipens taking a meal|
It has evolved very recently, certainly since the London Underground was built, starting in 1863, almost certainly from a population of C. pipens, and made life miserable for those who took shelter in London Underground stations during the blitz of WWII, as though Hitler wasn't making it miserable enough. The fact that hybrids between it and C. pipens are usually sterile suggests that speciation has occurred and the subterranean variety should more properly be classified as a new species rather than a variety or subspecies of C. pipens.
The evidence for this mosquito being a different species from C. pipiens comes from research by Kate Byrne and Richard Nichols. The species have very different behaviours, are extremely difficult to mate, and with different allele frequencies consistent with genetic drift during a founder event. More specifically, this mosquito, C. p. f. molestus, breeds all-year round, is cold intolerant, and bites rats, mice, and humans, in contrast to the above-ground species, which is cold tolerant, hibernates in the winter, and bites only birds. When the two varieties were cross-bred, the eggs were infertile, suggesting reproductive isolation.
I'd love a liar for Jesus/money/power from the Discovery Institute, Answers in Genesis, or any other pseudo-science creationist scam site to come here and explain to my readers how this fits with their infantile 'Intelligent (sic) Design' model. Why would a benevolent creator god suddenly come up with a subterranean mosquito in the last 150 years which seems to exist solely to make more mosquitos and for making the life of travellers, staff and maintenance workers on the London Underground a little less pleasant, unless he was on Hitler's side in WWII and was doing his bit to help by being an irritating little nuisance and has just left his secret weapon hanging around?